"all restaurants" and "all the restaurants"

Hi, please help me with this:

1/ what is the difference between “all the restaurants”, “all restaurants” and “all of the restaurants”?

2/ Mr Jones has been a worker in the first factory which began operation here for the past fifteen years
a. the factory is fifteen years old
b. he’s working at the factory now
c. he just stopped working at the factory
d. the factory began operation about five years ago
=> the answer for this is a, but I wonder why b is not right…

Hi,

The whole point of the definite article ‘the’ is, as the description indicates, that it defines and specifies. If you omit the article you are speaking generally if you include it, you are defining.

To me ‘a’ and ‘b’ both make sense.

What doesn’t make sense is this sentence:

which began operation here for the past fifteen years

Alan