毫无疑问，交易失败是他的错。

There is no ___question that it was his fault that the deal fell through.

线上学习是否同样有效仍有待商榷。

Whether online learning is as effective is still open to ___question.

新证据让人们对主要证人的可信度产生了怀疑。

The new evidence calls into ___question the reliability of the main witness.