【题目】All living flowers ultimately derive from a single ancestorlived about 140 million years ago, a study suggests.
A.why
B.what
C.where
D.that

【答案】D
【解析】考查定语从句。句意：一项研究表明，地球上现存的所有花卉都起源于1.4亿年前的同一个“祖先”。 空格前ancestor是先行词在定语从句中做主语。故选D。