Fill in the blank with the most appropriate option to complete the sentence:
He used to pray every day, believing that as long as he_____ so he would be safe.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → did
Sequence of tenses (a habit in the past):
- When the main verb is in the past, a clause that depends on it normally stays in the past.
- Clue words: "used to pray" shows a habit in the past, and "would be safe" is the past form of "will be". The blank in "as long as he ... so" must also be in the past: did (did so = prayed).
- Complete sentence: He used to pray every day, believing that as long as he did so he would be safe.
Example: She believed that as long as she worked hard, she would succeed.
Why the Other Options are Incorrect?
Option 1: is doing — Incorrect. The present continuous describes an action going on now; it clashes with "used to" and "would".
Example: He is doing his homework now.
Option 2: does — Incorrect. The simple present fits a present habit (as long as he does so, he will be safe), not a habit in the past.
Example: He does yoga every morning.
Option 4: will do — Incorrect. "Will" points to the future, and a clause beginning with "as long as" does not take "will" in any case.
Example: I will do it tomorrow.
Contrast: "used to" and "would" keep the clause in the past ("did"); "does" fits only a present habit ("as long as he does so, he will be safe").