The black box is a necessary device on an airplane, which records its speed, direction and whether everything on the airplane______ normally.

The black box is a necessary device on an airplane, which records its speed, direction and whether everything on the airplane______ normally.

The black box is a necessary device on an airplane, which records its speed, direction and whether everything on the airplane______ normally.

1. A.
   will function
2. B.
   functioned
3. C.
   is functioning
4. D.
   has functioned

The black box is a necessary device on an airplane, which records its speed, direction and whether everything on the airplane______ normally.

A. will function  B. functioned   C. is functioning   D. has functioned