例1：There were many guests at the party yesterday.I looked for two seats to sit down with my friend but found_____
A:neither B: nothing C:none D:no
例2：As land is improved by sowing it with various seeds ,_____is the mind by exercising it with different studies.
A:what B:that C:so D:such
例3：Traffic accidents _____ happen on such a snowy day .You can't be too careful while driving.
A:must B；can C:should D:shall
例4:I guarantee you ___be rewarded for any useful clues to the missing document of the local Health Department.
A:shall B:may C:have to D:would
例5:It is said that few situations are more annoying than struggling with a computer that ____start.
A:mustn't B:can't C: won't D: shan't
例6:Nancy says ,before the reader knows her reason for writing ,____you should not doubt what she is going to say .
A:that B:which C；why D:when
拜托告诉你做这题的理由依据，语法知识点务必要讲出来啊.....