——Be quiet! Mr Smith is coming.——Don't worry. It__________be him. Mr Smith is much taller.
A:mustn't
B:must
C:can't
D:needn't
彩色电视机荧光屏上呈现的各种颜色,都是由三种基本色光混合而成的,这三种基本色光是____ 、____ 、____ 。
对世界遗产应采取的态度是