Rule: Adjective + Preposition Collocation. The adjective 'susceptible' is always followed by the preposition 'to'. The phrase 'susceptible to something' means likely or liable to be influenced or harmed by a particular thing. This is a fixed grammatical pairing. Options (a) 'for', (b) 'of', and (c) 'with' are incorrect prepositions to use with 'susceptible'.

Rule: Vocabulary in a Legal Context. The phrase 'lack of evidence' suggests the defendant will be cleared of blame. 'Absolve' means to declare someone free from guilt, obligation, or punishment, which is the appropriate legal term. Option (a) 'accuse' and (b) 'convict' are antonyms of the required meaning. Option (d) 'activate' is irrelevant to the context.

Rule: Subject-Verb Agreement with 'A number of'. The phrase 'A number of' is followed by a plural noun ('applicants') and takes a plural verb. It is treated as a plural subject. In contrast, 'The number of' takes a singular verb. Therefore, the plural verb 'have' is correct. Options (a) 'has', (c) 'is', and (d) 'was' are all singular verbs.

Rule: Vocabulary - Choosing the Correct Adjective. The effect described (students falling asleep) indicates that the lecture was long, slow, or dull. 'Tedious' means too long, slow, or dull: tiresome or monotonous. This fits the context perfectly. Option (b) 'terrific' means excellent. Option (c) 'tactful' means having skill and sensitivity in dealing with others. Option (d) 'tenable' means able to be defended against attack or objection.

Rule: Conditional Conjunctions. This sentence presents a negative condition. 'Unless' means 'except if' and is used to introduce the only situation in which an event will not happen. 'Unless you work harder' means 'If you do not work harder'. Option (b) 'If' would require a negative verb in the clause ('If you do not work harder...'). Option (c) 'Although' introduces a contrast, which doesn't fit the logic. Option (d) 'Until' refers to time, not a condition.

Rule: Vocabulary in Context. The sentence requires a verb that means 'to reach a final result'. 'Culminated' means to reach a climax or point of highest development, which perfectly describes the outcome of long research. Option (a) 'cultivated' means to develop or acquire a quality. Option (c) 'calculated' means to determine something mathematically. Option (d) 'calibrated' means to adjust an instrument for accuracy. 'Culminated in' is the idiomatically correct phrase for this context.

Rule: Vocabulary - Adjectives for Lifestyle. The sentence contrasts wealth ('millionaire') with a simple way of living. 'Frugal' means sparing or economical with regard to money or food, which provides the intended contrast. Option (b) 'futile' means pointless or useless. Option (c) 'fragile' means easily broken. Option (d) 'fertile' means capable of producing abundant vegetation or offspring. 'Frugal' is the only adjective that describes a manner of living economically.

Rule: Vocabulary in Context. The sentence requires a verb that means to maintain something in its original state. 'Preserve' means to maintain and keep safe from harm or destruction. This fits the context of protecting cultural heritage. Option (a) 'perceive' means to become aware of or understand. Option (c) 'persevere' means to continue in a course of action despite difficulty. Option (d) 'presume' means to suppose that something is the case on the basis of probability.

Rule: Prepositional Phrasal Verbs. The verb 'refrain' is followed by the preposition 'from'. The phrase 'refrain from' means to stop oneself from doing something. This is a fixed collocation. Option (b) 'restrain' means to prevent from doing something, but it's typically used with an object (e.g., 'restrain him from...'). Option (c) 'detain' means to keep someone in custody. Option (d) 'contain' means to have something inside. 'Refrain from' is the idiomatically correct choice.

Rule: Vocabulary - Precise Verb Choice. The context is about making a secret known. 'Reveal' means to make previously unknown information known to others, which is the most direct and fitting word. Option (a) 'unravel' means to investigate and solve a mystery, which is a close synonym but 'reveal' is more direct about the outcome. Option (b) 'ravel' means to entangle or confuse. Option (c) 'revile' means to criticize in an abusive manner. Thus, 'reveal' is the best fit.