In the following sentence, choose the correct phrasal verb or expression to complete the blank so that the sentence sounds natural and grammatically correct: The doctor has been ____ to attend to an urgent case.

Introduction / Context:
This item is a question on phrasal verbs and typical collocations used when summoning a professional to perform a duty. In everyday and formal English, certain verbs combine with small words like in, on, over, or off to form phrasal verbs with special meanings. For example, call in a doctor means request a doctor to come, while call off means cancel something. The sentence here describes a situation where a doctor is needed urgently, so the correct phrasal verb must reflect this idea.

Given Data / Assumptions:

The sentence is: The doctor has been ____ to attend to an urgent case.

The context is that someone requested the doctor to come.

We assume that the request has already been made, as indicated by has been.

The phrase attend to an urgent case confirms that medical help is required.

We need the most natural and idiomatic expression.

Concept / Approach:

Phrasal verbs in English are often fixed and must be learned as set phrases. The verb call has many combinations: call in, call out, call off, call over, and so on. The usual expression when requesting a specialist like a doctor, mechanic, or expert is to call in that person. In passive voice, we say The doctor has been called in. Other combinations either change the meaning completely or do not fit this context. Therefore, we must test each option against actual usage and meaning.

Step-by-Step Solution:
Step 1: Insert option a: The doctor has been called to attend to an urgent case. This is grammatically acceptable and sometimes used, but the exam usually prefers a phrasal verb in this structure. Step 2: Insert option b: The doctor has been called in to attend to an urgent case. This is a very common and natural expression when someone is summoned to deal with a problem. Step 3: Insert option c: The doctor has been called over to attend to an urgent case. Called over suggests calling someone from a nearby place, not formally requesting a doctor. Step 4: Insert option d: The doctor has been called by to attend to an urgent case. Called by is not used in this way and sounds wrong. Step 5: Insert option e: The doctor has been called off to attend to an urgent case. Call off means cancel, so this makes no sense. Step 6: Compare called and called in and choose the option that best matches the exam focus on phrasal verbs.

Verification / Alternative check:

We can check by looking at similar examples: A specialist was called in to repair the machine or The manager was called in to resolve the dispute. In each case, called in means requested to come and deal with an issue. The pattern The doctor has been called in to attend to an urgent case matches these examples exactly. This confirms that called in is the best choice among the given options.

Why Other Options Are Wrong:

Option a (called) is grammatically possible, but it does not highlight the phrasal verb usage the question is designed to test, and is less specific than called in.

Option c (called over) tends to refer to calling someone from a short distance, often informally, and does not fit the formal tone of an urgent medical case.

Option d (called by) is incorrect in this context because call by usually means to visit briefly, not to be summoned.

Option e (called off) means to cancel something, which is opposite in meaning to what is needed here.

Common Pitfalls:

Learners often treat all phrasal verbs with call as interchangeable and may choose based on guesswork. Another common mistake is to ignore the subtle difference between call and call in, where the latter has the stronger sense of summoning an expert. To avoid errors, it is useful to associate phrasal verbs with typical collocations, such as call in a doctor, call off a meeting, or call up a friend.

Final Answer:

The most appropriate phrasal verb in this context is called in.