问几道英语单选题,希望得到分析解答

题目

问几道英语单选题,希望得到分析解答
1.when he entered the room,he dound Mary ___at the desk,reading.
A.seating .B.sat.C.seated.D.sitting herself
为什么不选B,A看起来也可以吧,前面不是有when么..
2.it has been announced that candidates(候选人)___remain in their seats until all the papers have been collected.
A.can/ C.could/ C.may/ D.shall
惭愧没看懂,为什么不能选其他选项,我看哪个都差不多...
3.on no condition __such unfair conditions.
A.will we accept / B.we will accept
C.we are to accept / D.are we accepted
怎么那么多condition,为什么不能选A
4.rf
1楼能回答的详细一点吗,2楼的你不会就不用答了,

答案

1、seating 是使就座的意思,find sb.doing sth.
2、 宣布所有的选手要坐在座位上直到试卷全部收齐 选D
3、on condition 是在……的条件下,on no condition 就是决不要,没任何条件.unfair condition 是不公平的条件