Cable TV began in 1948 in the USA, but it took 50 years ________ 66 percent of American households

had it.

Cable TV began in 1948 in the USA, but it took 50 years ________ 66 percent of American households
had it.

Cable TV began in 1948 in the USA, but it took 50 years________ 66 percent of American households had it．

A．before         B．after          C．unless         D．since

Cable TV began in 1948 in the USA, but it took 50 years ________ 66 percent of American households had it.

1. A.
   before
2. B.
   when
3. C.
   after
4. D.
   until

 Cable TV began in 1948 in the USA, but it took 50 years________ 66 percent of American households had it.

A. before                    B. after                      C unless                     D. since