防治草场退化的重要措施有
①科学养畜；②建设人工草场；③培养优良牧草；④划区轮流放牧。[ ]
A．①
B．①②
C．①②③
D．①②③④
答案：D
Bats are surprisingly long-lived creatures, some ___ a life span of around 20 years.
A．have
B．had
C．having
D．to have
—Do you often play____________soccer with your friends?
—No, I don't like sports. I often play____________piano in my free time. [ ]
A. a, the
B. the, /
C. /, the
D. the, a
