4.Howare they opened? How are they closed?
举一反三
- The noise of the desks _____ could be heard in the next classroom. A: being opened and closed B: opened and closed C: having been opened and closed D: to be opened and closed
- The noise of desks___could be heard out in the street. A: opened and closed B: to be opened and closed C: being opened and closed D: having been open and closed
- At the beginning of the class,the noise of desks ________could be heard outside the classroom. A: opened and closed B: to be opened and closed C: being opened and closed D: to open and close
- A．openedB．closedC．openD．close A: opened B: closed C: open D: close
- Each cylinder has one starting valve which is usually opened by air pressure and closed by （）