The number of teachers in this school（）unknown.

单项选择题A number of paintings in the castle are believed( )( )( )in a fire.being destroyedB. having been destroyedC. to be destroyedD. to have been destroyed

单项选择题Middle school boys( )( )( )not to smoke.

单项选择题The class ( )( )( ) over, we had a ( )( )( )discussion.

单项选择题We specialize ( ) the exportation of Chinese light industrial products.

单项选择题The method is ( ) cheaper and safer.

单项选择题Which of the following choices is not the compulsory component of business letters?

单项选择题I would like to take advantage ( ) the discount to place an order with you.

单项选择题Which of the following is focused on writing?

单项选择题To cultivate communicative competence, what should correction focus on?

单项选择题What should a required lesson plan look like?