如图是一个半圆形桥洞截面示意图,圆心为O,直径AB是河底线,弦CD是水位线,CD∥AB,且AB=26m,OE⊥CD于点E.水位正常时测得OE:CD=5:24
Bill doesn't like the sunglasses in the ad because they can't __________ the sun well.
等差数列{an}中,a3+a4=4,a5+a7=6.
如图,□ABCD中,EF∥AB,DE∶EA = 2∶3,EF = 4,则CD的长为( )
以下动物中,属于软体动物的是( )