Thanks for teaching! You help me a lot.

you are not as lazy as him OR as he is mary is prettier than she is OR than her you have the same role as I do OR as me As Michael says below: essentially if you are using the subject pronoun you must use a verb. if you are using an object pronoun, you must not use a verb.

Your text book is not very clear. B Could easily be "Mary is prettier than she is." Using the book's logic of "leaving out", then B is exactly correct. In modern English, though, we tend to choose between the "correct" (in old grammar) subject pronoun with verb ( "than she is", "as he is", "as I am") or the now-standard and also correct, I think, object pronoun on its own; "than me", "than her", "than him". Have a look at this link: https://www.merriam-webster.com/words-at-play/than-what-follows-it-and-why I should add that I have just looked online, and there are quite a lot of inaccurate sources on this, so your grammar book is not alone. In English we do not have any final authority on grammar - no Academy or government department to announce what is true. Most grammarians, I think, regard Merriam-Webster and the Oxford English Dictionary as being as close as we get to authoritative sources. perhaps adding The British Council, and the dictionaries from Longmans, Collins and Cambridge. https://motivatedgrammar.wordpress.com/2012/06/13/than-i-and-than-me/