Television first appeared some fifty years ago in the 1950s. Since then, it has been one of the most popular sources of entertainment for both the old and the young. Television offers cartoons for children, world news, music and many other programs. If someone is interested in sports, forinstance, he can just choose the right sports channel. There he can enjoy a broadcast of an international football match _______ it is actually happening. Television is also a very useful way for companies to advertise their products.

It is not too hard for us to see why there is a TV set in almost every home today. And, engineers are developing interactive TVwhich allows communication between viewers and producers

Giải thích tại sao lại chọn liên từ vậy 

$A. as$

$B. so$

$C. amd$

$D. or$