We have bought . . . . . . . . LCD television set. A. a B. an C. the D. no article

The correct answer is: D. no article

We use no article before a general noun that refers to a class of things, not a specific thing. In this case, the speaker is not referring to a particular LCD television set, but to LCD television sets in general.

We use “a” or “an” before a singular common noun that refers to a specific thing. In this case, the speaker could be referring to a specific LCD television set that they have bought.

We use “the” before a singular common noun that refers to a specific thing that is already known to the listener. In this case, the speaker could be referring to a specific LCD television set that they have already mentioned.