题文
Scientists are convinced _ the positive effect of laughter physical
and mental health.
| A．of; at |
| B．by; in |
| C．of; on |
| D．on; at |
推荐试卷
Scientists are convinced _ the positive effect of laughter physical
and mental health.
| A．of; at |
| B．by; in |
| C．of; on |
| D．on; at |
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