几道考研的题.请大家帮帮忙.用括号里的词填空.谢谢.

几道考研的题.请大家帮帮忙.用括号里的词填空.谢谢.
1.They knew that in 1935 that Mrs Simpson was ____ a lover other than the next King.(entertain)
这题应该填啥呢?entertaining还是entertained...为啥呢?
2. ___ within a species is the raw material upon which natural selection acts.（vary）
这题填什么以及怎么翻译.
3.Saved up to 50% on phone fares when ____ on line.(book)
这题应该是booked 还是booking呢?为什么?
谢谢各位高手.