**Rule**: The **Present Perfect Continuous Tense** is used for an action that started at a specific time in the past ('since yesterday') and is still in progress. The word 'police' is a plural noun. **Correct Usage**: 'have been searching' correctly describes the continuous, ongoing search that started yesterday. **Incorrect Options**: (a) 'search' (Simple Present) is a habit. (b) 'are searching' (Present Continuous) is correct for an ongoing action but doesn't incorporate the starting point 'since yesterday' as well. (d) 'searches' is a singular verb.

**Rule**: The **Present Continuous Tense** is used to describe a weather condition that is happening at the moment of speaking, especially when there is visible evidence ('the trees are swaying'). **Correct Usage**: 'is blowing' correctly describes the current, ongoing action of the wind. **Incorrect Options**: (a) 'blows' (Simple Present) is a general statement. (c) 'has blown' (Present Perfect) is a completed action. (d) 'has been blowing' would emphasize the duration.

**Rule**: The **Present Continuous Tense** is used to describe an event that is in progress at the moment of speaking. **Correct Usage**: 'is setting' describes the process of the sun going down, which is happening right now. **Incorrect Options**: (a) 'sets' (Simple Present) is a general fact. (c) 'has set' (Present Perfect) means the sun is already down. (d) 'set' (base form) is grammatically incorrect.

**Rule**: The **Present Continuous Tense** in the negative is used to describe something that is failing to function correctly at the present time. **Correct Usage**: 'isn't showing' correctly describes the current malfunction of the watch. 'Doesn't show' is also possible, but 'isn't showing' emphasizes the current, temporary problem. **Incorrect Options**: (a) 'doesn't show' (Simple Present) is also a good option. (c) 'hasn't shown' (Present Perfect) refers to the time up to now. (d) 'not show' is incomplete.

**Rule**: The **Present Continuous Tense** with 'always' is used to express annoyance or criticism about a repeated action. The structure is **am/is/are + always + verb-ing**. **Correct Usage**: 'are you always complaining' conveys a sense of irritation about a frequent habit. **Incorrect Options**: (a) 'do, complain' (Simple Present) would be a neutral question about a habit, lacking the nuance of annoyance. (c) 'have, complained' (Present Perfect) asks about past instances. (d) 'did, complain' (Simple Past) asks about a specific past event.

**Rule**: **Stative Verbs**. When 'think' is used to express an opinion, it is a stative verb. The negative is formed with **'do/does not + think'** in the Simple Present. **Correct Usage**: 'I don't think' is the standard way to express a negative opinion. **Incorrect Options**: (a) 'am not thinking' would be used for the active mental process. (c) 'haven't thought' refers to a lack of thought in the past. (d) 'no think' is grammatically incorrect.

**Rule**: The **Present Perfect Tense** is used with stative verbs (like 'know', 'like', 'be') to describe a state that began in the past and continues into the present, especially with a duration like 'for a long time'. **Correct Usage**: 'have known' is the correct form to express this continuous state of knowing from the past until now. **Incorrect Options**: (a) 'know' (Simple Present) is grammatically possible but lacks the emphasis on duration. (b) 'am knowing' is incorrect because 'know' is a stative verb. (d) 'has known' is for third-person singular subjects.

**Rule**: **Stative Verbs**. 'Consist' is a stative verb describing composition. It is not used in continuous tenses. The **Simple Present** is used to state a fact. **Correct Usage**: 'consists' correctly states a fact about the sweater's material. The subject 'This sweater' is singular. **Incorrect Options**: (b) 'is consisting' is grammatically incorrect. (c) 'has consisted' is the wrong tense. (d) 'consist' is a plural verb.

**Rule**: The **Present Perfect Tense** in the negative with 'yet' is used to show that an expected action has not happened up to the present time. This lack of completion has a direct present result. **Correct Usage**: 'hasn't finished' is the correct form. The present result is 'he can't go out'. **Incorrect Options**: (a) 'doesn't finish' (Simple Present) is a habit. (b) 'isn't finishing' (Present Continuous) is for the current moment. (d) 'didn't finish' (Simple Past) would need a specific past time frame (e.g., 'he didn't finish it last night').

**Rule**: The **Present Perfect Tense** is used in negative sentences with 'yet' to indicate that an action has not happened up to the present time, within an unfinished time period ('this month'). **Correct Usage**: 'haven't paid' correctly expresses that the payment has not been made in the period from the beginning of the month until now. **Incorrect Options**: (a) 'don't pay' (Simple Present) implies a habit of not paying. (b) 'am not paying' (Present Continuous) refers to the present moment. (d) 'didn't pay' (Simple Past) would refer to a finished time period, like 'last month'.