In this idiom question, choose the alternative which best expresses the meaning of the phrasal verb “fall back on”.

Introduction / Context:
“Fall back on” is a common phrasal verb used in everyday English and in formal writing. It appears frequently in discussions about finances, support systems and backup plans. Exam questions often test whether you know the precise meaning of such phrasal verbs. This item asks you to choose the option that best captures the meaning of “fall back on” in simple, clear language.

Given Data / Assumptions:

• The phrasal verb is “fall back on”.
• The task is to choose its closest meaning.
• The options are: retreat, overtaken, suffer an accident, resort to something.

Concept / Approach:
The expression “fall back on” does not refer to literally falling or moving backward. Instead, it refers to using something for help or support when the first choice has failed. For example, people may fall back on savings when they lose a job, or students may fall back on memorised notes when understanding fails. Thus the core sense is to “resort to” some backup resource or option. Among the given alternatives, we must pick the one that expresses this idea most directly.

Step-by-Step Solution:
Step 1: Fix the meaning of “fall back on” as to use something as a last resort or backup support. Step 2: Examine option a) “retreat”. This means to move back or withdraw, usually in a physical or military sense. It does not mention using a backup resource. Step 3: Examine option b) “overtaken”. This describes being passed or caught by something or someone and is unrelated to the idea of using a backup. Step 4: Examine option c) “suffer an accident”. This is completely unrelated in meaning to relying on support or backup. Step 5: Examine option d) “resort to something”. This fits perfectly, because to resort to something is to turn to it for help when other things fail. Step 6: Conclude that option d) correctly explains the phrasal verb.

Verification / Alternative check:
Consider the sentence: “When his business failed, he had to fall back on his savings.” Replace “fall back on” with “resort to” and you get, “he had to resort to his savings”, which has the same meaning. If you try replacing it with “retreat”, “overtaken” or “suffer an accident”, the sentence becomes meaningless. This quick substitution test confirms that “resort to something” is the correct explanation.

Why Other Options Are Wrong:
“Retreat” focuses on moving back, not on using a backup resource. “Overtaken” refers to being passed or caught up and shares no semantic overlap with the idiom. “Suffer an accident” is completely unrelated and is included to test whether you are paying attention to the phrasal verb as a whole rather than just the word “fall”. These distractors highlight the importance of learning phrasal verbs as fixed combinations whose meanings cannot always be predicted from individual words.

Common Pitfalls:
Many learners incorrectly guess meanings of phrasal verbs by focusing on only the main verb, here “fall”. They may connect it with physical movement or failure and miss the actual idiomatic sense. Another pitfall is guessing based on partial recall of similar expressions like “fallback position”, which indeed refers to a backup plan but may confuse the learner. The safest way is to memorise high-frequency phrasal verbs with short definitions and example sentences, then regularly revise them.

Final Answer:
“Fall back on” means to resort to something as a backup or last resort.