经角膜曲率仪测定,诊为角膜和晶状体混合性散光,适用()镜片。
A、内环曲面外球面
B、内外双环曲面镜片
C、外环曲面内球面镜片
D、内外双球面镜片
参考答案:B
________ people are concerned about now is the Shanghai World Expo, which ________ start on May 1st.
A.What; is due to
B.Which; is going to
C.That; is to
D.What; is about to
简述中国数学会的建立过程。