在大熊猫和大肠杆菌体内，最基本的化学元素和含量最多的化学元素分别是[ ]
A．C和O
B．C和H
C．O和C
D．H和O
答案：A
Because the shop _____, all the T-shirts are sold at half price.[ ]
A. has closed down
B. closed down
C. is closing down
D. had closed down
目前奥运会跆拳道比赛采用三回合制，每个回合（）分钟，回合之间休息（）分钟.
A、3；1
B、2；1
C、3；2
