Scientists are convinced_____the positive effect of laughter_____physical and mental health

Are there any books related to the situation around Diaoyu Island?—There’re only a few, ________.

_______ worries the public a lot the way thestudents are getting more and more stressed out

I can’t go for a picnic with you becausesomething urgent has _____ —What a shame!

When we first met on a train in 2000, we both felt immediately that we _____ each other for years. [ ]