'Pull someone's leg' is an idiom, it means 'to tease someone'. For example, 'Stop pulling my leg!' (stop teasing me!). Hence option A is correct, as it means the same as the idiom.
Idiomatic expressions do convey a literal meaning; 'pulling someone's leg' does not mean to literally pull a person's limbs, or trip a person.
Option B has no relation to the given idiom; hence options B, C and D are incorrect.
(As idioms are devoid of literal meaning and are mainly
constructed to describe something different, Option A holds true. Rather
than focusing on the physical aspect, this idiom means to verbally
tease another person in a comic way.)