30．Are you certain that this is _________in his speech

One theory, ________ suggested by Harvard University, is that humans began cooking their food, thereby releasing nutrients locked in the raw food and reducing the time needed to chew it.

He is a man who lacks experience and determination, and I think he is not________the job. [ ]

I often hear the girl_______ beautifully next door. When I passed the door, I heard her _______ just now.

Paul attends very ________ meetings，and when he does，he has very ________ to say．