Scientists are convinced _____ the positive effect of laughter _____ physical and mental health.[ ]

The stamps, once ________, will be very popular with stampcollectors[ ]

I’m really very busy，otherwise I ________ certainly go there with you.

The window ______ by Tom yesterdayMrWhite is repairing it now

Timmy often gets full marks in the exams, but he nevershows off. He is very ______.