问题补充：
It’s so silly people to buy and store so much salt. It’s necessary them to learn more about salt.
A. for; for
B. for; of
C. of; of
D. of; for
答案：
A. for; for
B. for; of
C. of; of
(答案→)D. of; for
解析：表示对于某人进行评价，用It’s +adj+of sb +to do sth，而对于做某件事是怎样的用句型It’s +adj+for sb to do sth，故选答案为D
