1.These_(this) books are Mary's
books 是复数,而this的复数是these
2.There are lots of mankeys in the zoo and_they_(it)are cute
猴子mankey,它加了s表明了是复数,it的复数是they
3.This cat is _your_(you)cat
你的猫,you (你;你们)应换成your(你的；你们的)
4.David_has_(have)a funny book
第三人称转述的单数应用has
5.There are lots of_photos_(photo) in the book
There are是复数形式,所以photo应变成photos.原本以o结尾的后面应加es,但是photo是photograph的简写,所以复数应是photos.