用换元法解方程2xx2-1-3x2-3x=1，若设xx2-1=y，则原方程可化为

Vegetables are _____.[ ]

A. bad for you    

B. not good      

C. good for you  

D. bad

. — Did you take enough money with you?

— No, I needed _______ I thought I would.

A．not so much as

B．as much as

C．much more than

D．much less than

属于煤气特点的有（）

A.易中毒

B.易爆炸

C.易着火

D.有臭味

在正常使用条件下，屋面防水工程、有防水要求的卫生间、房间和外墙面的防渗漏，最低保修期限为3年。

每标准立方米天然气的发热值约为（）。

A.34kJ

B.34MJ

C.100kJ

D.100MJ