—She is a lovely girl, though she ________be naughty sometimes.
A:should
B:must
C:need
D:can
(____) What does your mother do?
(____) Oh, great!
(____) She's a nurse.
(____) Look! This is my mother.
(____) Oh! She's beautiful.
唐朝时发明的筒车,主要优势体现在( )