Definition: not probable Level: B2
他明天能否出席会议还很难说。
It is ___doubtful whether he'll be able to attend the meeting tomorrow.
丢失的钥匙不太可能找回来了。
It was ___doubtful that the lost keys would be recovered.
声称成功完全取决于天赋，这不太可信。
It is ___doubtful to claim that success depends solely on innate talent.
