D.
原因：英語中“因?yàn)椤薄八浴蓖ǔＶ挥靡粋€(gè).有because,since就不用so.
It 為虛擬主語,實(shí)際主語為“That he succeeded in the end" (記得加”that“哦,否則就不是句子成分,而成了獨(dú)立的句子了）.去掉虛擬主語的話,句子為：That he succeeded in the end was because he worked hard and persistently.
A.Since he worked hard and persistently,he succeeded in the end.
B.Because he worked hard and persistently,he succeeded in the end./
He worked hard and persistently,so he succeeded in the end.(不太常見這么說的）
C.As he worked hard and persistently,he succeeded in the end.