题目内容
Some experts have said that ________ children believe they can succeed, they will never become totally confident of themselves.
A.if B.since
C.once D.unless
D
【解析】D 考察状语从句。根据语境可知,unless引导条件状语从句,if如果,since自从,once曾经,一旦;句义:一些专家说,除非孩子们相信他们能够成功,否则他们永远不会对自己完全自信。故D正确。
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