Selling cost have to be incurred in case of

In the following question, out of the four alternatives, select the alternative which best expresses the meaning of the idiom/phrase.

At somebody's expense

The space shuttle which took Sunita Williams beyond earth was

Which one of the following is not a non-conventional source of energy?

In IT, the method for updating the main memory as soon as a word is removed from the cache is called

In an optical fibre the signal is transmitted

Which one of the following processes is responsible for the glittering of air bubble rising through water?

What causes the mottling of the dental enamel ?