4. One day, there are two exciting TV programs, A and B. A survey of 560 viewers shows that the ratio of the number of viewers who watch both programs to the number of viewers who watch program A to the number of viewers who watch program B is $1: 2: 3$. In this survey, the number of viewers who watch program A is $(\quad)$ people.
A. 280
B. 420
C. About 433
D. About 373
4. A.

Let the number of viewers who watch both programs be $x$, then $x+(2 x-x)+(3 x-x)=560$, so $x=140$ (people).