若a是int型变量、且a的初值为6,则执行下面表达式后,a的值为()。a+=a-=a*a
参考答案:60
Great changes ____________ in my hometown in the past few years.
A.took place
B.have taken place
C.have been happened
D.broke out
加氢反应器的类型有哪些?