几道语法题请教？

lxy1120

兔兔，有个疑问：
P152.13的结构是A do something more effect ...than do B...
P168.34 Because its body (is supported) by water, the blue whale can grow to a size (considerable) larger (than any) land mammal (alive) today.简化为：A can grow to a cnsiderablly larger than B ，这里为何than后面不用can B?
关于比较级中助动词的补出，一直有这个疑问，不知什么情况下要补出助动词，什么情况下不用？

lxy1120

3X！GMAT语法一直不好，谢谢你给补了这一课。