I could not distinguish the original … the fake.

Analyze the question: The sentence is "I could not distinguish the original ......... the fake." We need the correct preposition after the verb distinguish when comparing two things.

Explain the concept: The verb distinguish is followed by from when you separate or tell one thing apart from another:

• distinguish A from B = tell A apart from B
• Example: "A child must learn to distinguish right from wrong."

You can also say "distinguish between A and B," but you cannot say "distinguish A to B," "by B," or "with B."

Step-by-step solution:

1. The sentence compares two things: the original and the fake.
2. The structure needed is "distinguish [thing] ___ [other thing]."
3. Test each option: • A. from: "distinguish the original from the fake" ✔ (correct idiom) • B. to: "distinguish the original to the fake" ✘ (wrong; to is used in "similar to" or "compare to") • C. by: "distinguish the original by the fake" ✘ (this would suggest using the fake as the means of identifying the original) • D. with: "distinguish the original with the fake" ✘ (not idiomatic)

Answer: The correct option is A. from.

Exam tip: Remember the pair "distinguish ... from", just like "differ from," "separate from," and "tell ... from." Verbs of separating or telling apart usually take from. In the exam, test each preposition by reading the whole sentence aloud. The wrong ones will sound odd.