A:may be
B:might have bee
C:may not be
D:mightn’t have bee
算一算
7×3=____27÷9=____32÷8=____25+6=____31-8=____
24÷4=____6×7=____49÷7=____20÷4=____42÷7=____
如图,直线AB与⊙O相切于点C,D是⊙O上的一点,∠CDE=22.5°,若EF∥AB,且EF=2,则⊙O的半径是 ____.