A:9
B:
C:-9
D:-
裸子植物和被子植物的主要特征是( )
- Junior high school days will be over _______ a week. How are you feeling?
- I'm trying to keep my cool because we've been together ________ three years.
如图所示的实验装置,将两根阻值不等的电阻丝R1、R2串联后分别放入两个透明容器中,并封闭等量的空气,通电前,A、B两U形管内的液面相平,接通电源一分钟后,通过A、B两个U形管内的液面相比较( )