Now it's time us a story.[ ]
A. tell
B. to tell
C. tells
D. telling
答案：B
— There must be a dozen pens in the room,but I can never find one when I need them.
— Keep looking. _____ is sure to turn up. [ ]
A. One
B. It
C. That
D. This
DNA的成分是
A．脱氧核糖核酸B．核糖核酸C．氨基酸D．多肽E．核蛋白
