青少年正处于生长发育的关键时期,下列饮食中正确的是( )
A:每天想吃什么就吃什么
B:只吃蔬菜,不吃鱼肉
C:吃少量的饭,主要依赖喝牛奶
D:按“平衡膳食宝塔”定时进餐
The teacher kept students _______ books for half an hour.
下列关于核糖体的叙述,正确的是
What were you ____(do) at nine o'clock yesterday morning?