立体构成的特征是（）
A.光影感
B.空间感
C.动感
D.都对
参考答案：D
______ young trees have been planted here, now it is a really beautiful place.
A．Hundred
B．Hundred of
C．Hundreds
D．Hundreds of
异分母分式相加减，先________变为________分式，然后再加减.
