减数分裂四分体时期,若细胞内有4个四分体,则其所含的脱氧核苷酸链共有( )
The students listened carefully to the teacher with their eyes _____ on the blackboard.
With our knowledge practice , we can make contribution to our society.
The most popular food ______ on menus in western countries is hamburger.
There is no greater pleasure than running on the playground, ____ after a ball.
I tried all I could_____ the topic at the meeting, but he brought it up.