Scientists are convinced ________ the positive effect of laughter ________ physical and mental health.
| A．of; at | B．on; at | C．by; in | D．of; on |
_____60 miles a day，you need your mountain bike in a very good state.
| A．Cover | B．Covered | C．To cover | D．Having covered |
-Did you attend Mary and Tom’s wedding ceremony?
-Yes，but as you know，they________each other no more than 3 months．
| A．knew | B．had known | C．have known | D．have been knowr |
_____I like the color of the hat，I don,t like its shape．
| A．While | B．If | C．How | D．When |
-We need a drink．I'm really thirsty
-_______．Let,s have one．
| A．Generally | B．Strictly | C．Exactly | D．Possibly |
They left without leaving a message，_____was more than we had expected．
| A．what | B．which | C．that | D．when |