When you visit a museum you must ask for _____ before taking photographs inside it.
Many things _______ impossible in the past are very common today.
The students in the university are all taking courses _______ a degree.
. _______ different kinds of pianos, the workers farther improved their quality.
A person _______ a foreign language must be able to use the foreign language _______ all about his own.
.The wallet _______ several days ago was found _______ in the dustbin outside the building.