对于接触网环形预应力混凝土支柱,预应力主筋的混凝土保护层厚度不应小于()。
A.10mm
B.15mm
C.20mm
D.25mm
参考答案:C
After school we usually play _____ basketball for half an hour on _____ playground. [ ]
A. the; the
B. /; /
C. /; the
D. the; /
广州出名的泮塘五秀是指哪些?