14．How can you cross the river _________ by swimming?

Our teacher is always busy preparing lessons until 11 o’clock at night, we students have gone to sleep.

He even ___________ notices at the supermarket to ask for old bikes.

李明同学说话喜欢引经据典，他引用的古诗文恰当得体的一项是

No matter how frequently ________,the works of Beethoven still attract people all over the world.