已知圆锥的侧面展开图是一个半圆,则母线与高的夹角是( )。
30°
After ten years abroad, he still recognized his old colleagues ________ he set foot in China.
A.immediately
B.for the first time
C.while
D.moment
某溶液的pH=9.6,则该溶液( )
A.呈中性
B.呈酸性
C.呈碱性
D.无法判断