1.If n is a positive integer and the product of all the integers from 1 to n,
inclusive, is a multiple of 990, what is the possible value of n ?
A.8
B.10
C.12
D.14
E.16
2.If a < b < 0, which of the following numbers must be positive?
Indicate all such numbers.
A.a-b
B.a^2-b^2
C.ab
D.a^2xb
E.a^2+ab^2
第一題不懂題目的意思，選了990的因數10
答案是CDE
第二題答案是BC
想問E選項除了直接代數字（有些代入是正有些是負，剛好代到都是正）
之外有沒有其他方法？
謝謝大家。