He has some books on the desk, but _______ of them is on history.
A:all
B:neither
C:none
D:both
在△ABC中,∠A,∠B,∠C的对边分别为a,b,c,如果c=2a,∠B=45°,那么∠C等于( )
What does the boy plan to do for his mother on Mother's Day?
有关DNA的叙述,正确的是( )