1) A is different from B and is correct because the if you look at the top view of the object, the part of the object on the top does not extend all the way to the right edge. The picture in B suggests that this top part does extend to the right edge, while A does not making it the right answer. Does that make sense?
2) I think D is suggesting that the point of contact of that little extension is circular, but nothing suggests that its circular and looks square from the pictures they give you. Also it looked like the portion that is furthest right on answer D is dashed meaning it would be behind something, and it is not.
Its hard to describe it in words, but I hope that helps.