Believe it or not did I hear it but also saw it.A. as wellB. not onlyC. never beforeD.

问题补充：

Believe it or not, did I hear it, but also saw it.

A. as well

B. not only

C. never before

D. only if

答案：

A. as well

(答案→)B. not only

C. never before

D. only if

解析：考察倒装句。Not only…but also…不但…而且…;not only放在句首，要部分倒装。AD两项放在句首，不要倒装。C项与现在完成时连用，表示倒装。故B正确。