Either the ways or the time _____ yet,but you may ask the headmaster for some information.A.isn't decided B.hasn't decided C.aren't decided D.haven't decided 为什么不选B?yet 不是用于完成时吗?

Either the ways or the time _____ yet,but you may ask the headmaster for some information.A.isn't decided B.hasn't decided C.aren't decided D.haven't decided 为什么不选B?yet 不是用于完成时吗?
Either the ways or the time _____ yet,but you may ask the headmaster for some information.
A.isn't decided B.hasn't decided
C.aren't decided D.haven't decided
为什么不选B?yet 不是用于完成时吗?

Either the ways or the time _____ yet,but you may ask the headmaster for some information.A.isn't decided B.hasn't decided C.aren't decided D.haven't decided 为什么不选B?yet 不是用于完成时吗?
其实这道题不用看yet.此空一看就应用被动语态,排除BD,另外,either…or…引导的句子,谓语动词用单数,即可知选A
既然你问了yet,就说一下吧~
yet
adv.
1.还,尚,仍然2.已经3.甚至,更4.现在；即刻；马上 5.从现在起直至某一时间；还6.（表示将来可能发生,尽管现在似乎没有可能）早晚,总有一天7.迄今为止,到当时为止（最好的或最长的等） 8.（强调次数或数量的增加） 9.（强调程度的增加）更 10.（用于否定句和疑问句,谈论尚未发生但可能发生的事）
conj.
1.然而,但是
当yet表示已经、迄今为止时,用完成时.
从后面半句来看,此处yet的意思为“用于否定句和疑问句,谈论尚未发生但可能发生的事”,故,用一般式即可.

方法和时间是被决定的，A 表示被动，B不能表被动 不能只看yet

如果是B的话，它是表示完成时，但是这道题的主语是什么？“The ways , the time ”它应该是主动去决定还是被人决定？“方式或时间”只能是被人决定，所以这里需要被动态。B必须是hasn't been decided 才是正确的。