Experts have been warning ___ of the health risks caused by passive smoking.

A.at a time                                                      B.at one time

C.for some time                                               D.for the time

Experts have been warning _____ of the health risks caused by passive smoking.

   A. at a time   B. at one time   C. for some time   D. for the time

 Experts have been warning    of the health risks caused by passive smoking

   A. at a time     B. at one time    C. for some time   D. for the time

 Experts have been warning ___ of the health risks caused by passive smoking.

A.at a time                             B.at one time

C.for some time                         D.for the time

Experts have been warning ____ of the health risks caused by passive smoking.

A. at a time　 B. at one time C. for some time　 D. for the time

Experts have been warning _______ of the health risks caused by passive smoking.

A. at a time　　 B. at one time　　　 C. for some time　　 D. for the time

Experts have been warning ________ of the health risks caused by passive smoking.

1. A.
   at a time
2. B.
   at one time
3. C.
   for some time
4. D.
   for the time