리딩 p.175,p.176 Grammer 17과

7. when working with chemicals, it is very impotant to take ............. measures against workplace accidents.

답: preventive

(왜 preventable은 안되는지?)

11.Ms. Stanislav asked for the documents in ............. the current trends of the Eastern European economy were described.

답:which

(왜 when,where는 안되는지?)

18. The contact information of customers to .................. the gift certificates are to be sent is included in the attachment.

답: whom

(왜 which,whose,whomever는 안되는지? 또, whomever는 어떻게 쓰이는지?)

24. Westwind Air has added more flights to its list of destinations .................. any other airline is the US has.

답:than

(왜 as 는 안되는지?)

너무햇갈려요~~

답변 부탁드립니다 ㅠㅠ