The chief engineer of the high-speed railway ________ Shanghai to Beijing always devotes most of his time ________ his work.
A:connecting; to
B:connects; to
C:connected; on
D:connect; on
在托盘天平的左盘垫上石棉网后放人一个打磨用的钢丝球,称出总质量。然后用电压为9伏的电池正负极轻触钢丝球,钢丝球迅速燃烧,并且左盘下降。下列叙述中,正确的是( )
下列关于卵细胞采集的叙述不正确的是( )