一道语法疑问

17．The Rorschzch test is gaining new repeat as a diagnostic tool because it takes only one hour to expose behavior and thought processes that may be unlikely to emerge in other procedures or weeks of ordinary interviewing.
(A) that may be unlikely to emerge in other procedures or weeks of ordinary interviewing
(B) whose emergence is unlikely in other procedures or weeks of ordinary interviews
(C) that might not emerge in other procedures or in weeks of ordinary interviewing
(D) that may not emerge under other procedures or weeks of ordinary interviewing
(E) unlikely not to emerge during weeks of ordinary interviewing or in other procedures

答案是c,a为什么不行呢？在or后的in不能省略吗？

A中的may be是口语，ets不提倡