详细解释几道SAT的语法题

题目

详细解释几道SAT的语法题
Studens in the origami class selected colorful sheets of paper,（creased and folded it carefully,and thus had created) fanciful animal shapes.
A.括号内原句
B.then creased and folded them carefully to create
C.they creased and folded it carefully to created
D.creasing and folding it carefully to created
E.creased and folded them carefully,thus they created
为什么选B而不选E?
(Preparing to be a foreign service officer) after graduation,both Mary and Keisha Have decided to major in international affairs.
A.原句
B.Because they wanted to prepare to be a foreign service officer
C.When preparing to be a foreign service officer
D.As preparation for becoming foreign service officers
E.Planning for their preparation to become foreign service officers
为什么选D而不选E

答案