把60分解质因数是[ ]
A.60=1×2×2×3×5
B.60=3×4×5
C.60=2×2×3×5
答案：C
you had better drop your parents a ________ in case (以防)they are worrying about you.
A．message
B．news
C．letters
D．line
所有权优势是指（）
A、管理技能
B、创新能力
C、劳动成本
D、资源禀赋
