在安装流量孔板时,孔板的各表面应()。
A、进行刮研;
B、绝对不允许打磨;
C、可倒去锐角;
D、可稍稍打磨。
参考答案:B
设f(x)是定义在R上的偶函数,且当x≥0时,f(x)=2x.若对任意的x∈[a,a+2],不等式f(x+a)≥f2(x)恒成立,则实数a的取值范围是________.
The boy __________ his dog well every day. [ ]
A. looks for
B. looks after
C. looks like
D. look after