The twins didn't go to the theatre, they _______ the light music all night.
A:have enjoyed
B:will enjoy
C:are enjoying
D:were enjoying
在显微镜下观察小鱼尾鳍内血液流动时,小动脉的辨别特征是( )
生物种子随“神舟七号”飞船在太空中飞行,通过这次飞行,可能使种子出现某种地球上无法获得的变异,而大大提升生物的品种质量,这种育种方法的原理是( )