**Rule**: The **Present Perfect Tense** is used to describe a recently completed action with a present or future relevance. **Correct Usage**: 'has written' indicates that the action of writing is finished, and the result is a new book that is ready for release. 'has been writing' would imply he is still in the process of writing it. **Incorrect Options**: (a) 'writes' (Simple Present) is a habit. (b) 'is writing' (Present Continuous) means he is writing it now. (d) 'has been writing' suggests the process is not yet complete.

**Rule**: The **Present Perfect Continuous Tense** is used to describe a continuous action over a recent period ('all week') that leads to a present feeling or situation ('we are looking forward to the weekend'). **Correct Usage**: 'have been working' emphasizes the continuous effort that has just finished or is about to finish, causing the present feeling. **Incorrect Options**: (a) 'work' (Simple Present) is a habit. (b) 'are working' (Present Continuous) is for right now. (d) 'worked' (Simple Past) disconnects the action from the present feeling.

**Rule**: **Stative Verbs**. 'Weigh' is a stative verb when it refers to the state of having a certain weight. It is not used in continuous tenses. **Correct Usage**: 'weighs' correctly describes a factual characteristic of the box. The subject 'This box' is singular. **Incorrect Options**: (b) 'is weighing' would only be used for the action of measuring weight (e.g., 'He is weighing the ingredients'). (c) 'has weighed' is the wrong tense. (d) 'weigh' is a plural verb.

**Rule**: The **Present Perfect Continuous Tense** is used to emphasize the duration ('all month') of an activity that leads to a present state ('is very stressed'). **Correct Usage**: 'has been studying' correctly links the prolonged period of study to her current emotional state. **Incorrect Options**: (a) 'studies' (Simple Present) is a habit. (b) 'is studying' (Present Continuous) is for now. (d) 'has studied' (Present Perfect) focuses on completion.

**Rule**: **Stative Verbs**. When 'have' means possession or to show a characteristic, it is a stative verb and is used in the **Simple Present Tense**. The subject 'The two brothers' is plural. **Correct Usage**: The plural verb 'have' agrees with the plural subject. **Incorrect Options**: (a) 'are having' and (d) 'is having' are incorrect because 'have' is stative. (b) 'has' is a singular verb.

**Rule**: The **Present Continuous Tense** is often used to talk about fixed personal arrangements in the near future. **Correct Usage**: 'are visiting' correctly describes a definite plan for the coming weekend. **Incorrect Options**: (a) 'visit' (Simple Present) is for habits. (c) 'have visited' (Present Perfect) refers to past visits. (d) 'visits' is for a singular subject.

**Rule**: The **Present Perfect Tense** is used to announce a recent event or change that has a result in the present. **Correct Usage**: 'has gone up' indicates a recent change (the price increase) with a present consequence (it's now more expensive). **Incorrect Options**: (a) 'goes up' (Simple Present) is a habitual action. (b) 'is going up' (Present Continuous) describes a trend in progress. (d) 'go up' is a plural verb.

**Rule**: Questions starting with 'How long' to ask about the duration of an unfinished action require the **Present Perfect Continuous Tense**. **Correct Usage**: The question asks about the duration of waiting that started in the past and is still ongoing. 'have you been waiting' is the correct question structure. **Incorrect Options**: (a) 'do, wait' is incorrect. (b) 'are, waiting' asks if they are waiting now, not for how long. (d) 'did, wait' is for a completed action in the past.

**Rule**: The **Present Continuous Tense** is used for an action that is in progress at the exact moment of speaking. The request 'Wait a moment' signals an ongoing activity. **Correct Usage**: 'am listening' correctly describes the action the speaker is engaged in right now. **Incorrect Options**: (a) 'listen' (Simple Present) is a habit. (c) 'have listened' (Present Perfect) means the action is finished. (d) 'have been listening' would emphasize the duration, which is not the focus here.

**Rule**: The **Present Perfect Tense** is used to describe a state that began in the past and has continued for a specific duration ('for a month now') up to the present. **Correct Usage**: 'has been' correctly describes the chef's continuous state of being at the restaurant for the past month. **Incorrect Options**: (a) 'is' (Simple Present) doesn't account for the duration. (c) 'was' (Simple Past) implies the state is over. (d) 'is being' is for temporary behavior.