Select the most appropriate preposition to fill in the blank.
We had to learn all the tables _____________ heart.

Correct option is D

Option (d) "by" is the correct preposition to fill in the blank. The phrase "learn by heart" is an idiom meaning to memorize something thoroughly.
· "By heart" is a common expression used to indicate that something has been memorized exactly, without needing to refer to notes or other aids.
· Example: She learned the poem by heart and recited it flawlessly.
Meanings of the other options:
· With (a): Used to indicate accompanying or possessing something; in this context, it would not fit with "heart."
· In (b): Used to indicate location or position within something; "in heart" does not make sense in this context.
· Within (c): Refers to something inside or enclosed by something else; again, "within heart" does not fit the context.
None of the other prepositions correctly complete the idiomatic expression "learn by heart."