—He ______ basketball with his friends.
A:plays
B:played
C:is playing
D:is plays
甲、乙两组同学举行拔河比赛,某段时间里,看到绳子被甲组同学匀速地拉过去,则此过程中 ( )
SARS病毒中有核酸____ 种,核苷酸____ 种,碱基____ 种.