For being a worker one has to fulfil all the activities listed below or one of them will do the job:-

1) engaged in legel economic activity.

2) the activity should be legal.

3) should be engaged in the production activity.

As per the definatation of the worker, a person who is engages in the productive activities and contributes to the GDP is considered as worker. Thus, option a is correct. In third optionif the production activities are just confined to the production activities and not to the service sector then it can not be true,

So, the correct option is A.