—What's the______ of the shoes?
—¥30. [ ]
A. number
B. sale
C. color
D. price
答案:D
维持蛋白质分子中β-折叠的化学键是 [ ]
A.肽键
B.疏水键
C.氢键
D.二硫键
E.离子键
It's time to .[ ]
A. have lunch
B. having lunch
C. lunch