小红把3x+7错写成3(x+7),结果比原来[ ]
A.多3
B.少3
C.多14
D.少7
答案:C
It's helpful _____ you to give me _____ useful advice. [ ]
A. for; so
B. of; such a
C. of; such
D. for; so a
频率与弦长成()比;频率与张力的平方成()比。