预应力混凝土主要是通过张拉预应力钢筋来预压混凝土，从而提高构件的抗裂度。( )
参考答案：对
My wife usually saves some money by ________ the prices of everything she buys.
A．turning down
B．cutting down
C．turning up
D．cutting up
Last year the number of students who graduated with a driving licence reached 200,000，a(n) ____________ of 40,000 per year.
A．average
B．number
C．amount
D．quantity
