Question

【題目】By the time he was fifteen years old, he ________ advanced maths all by himself.

A. had learned B. have learned

C. learned D. would learn

Answer 1

【答案】A

【解析】考查時(shí)態(tài)。句意：到他15歲為止，他已經(jīng)自學(xué)完了高等數(shù)學(xué)。by the time引導(dǎo)時(shí)間狀語(yǔ)從句，主句則表示在此時(shí)間之前某個(gè)事件已經(jīng)完成。當(dāng)從句用過(guò)去時(shí)，主句通常用過(guò)去完成時(shí)。由句意可知，在15歲之前，他已經(jīng)自學(xué)了高等數(shù)學(xué)。故該空應(yīng)用過(guò)去完成時(shí)態(tài)。