—So you gave Mary your dictionary?

— ______.She said she'd return it to me when she could afford her own.

蝉的身体长有外骨骼，下面哪项是外骨骼的重要作用

一列沿x轴正方向传播的简谐横波，在t=0时刻的波形如图所示．已知波的传播速度为1m/s，下列说法正确的是（   ）

She likes doing her homework _______ the radio _______.