The superlative degree of costly is costliest.

What is the superlative degree of the word "big is biggest.

what is the time by your watch?

What is the use of this statue?=  There is no use of this statue

Bacon wrote in his essay “Of Studies” that spend too much of time in studies is laziness or inactivity (sloth). Its mean that only study could not be fruitful without experience.

"River" is a common noun

The word knowledge is an abstract noun

A computer is an artificially intelligent machine that is programmed to work under fixed condition; But the human brain is naturally intelligent and it is able to operate on ever changing conditions.

What a nice fellow he is!

When he began to drink water, a wave swept him away. He was about to drown."

When he was four, he left his village (Make it complex). 

= At the age of four, he left his village.

When you think about the job.

Where have you come from ?

Where there is smoke, there is fire - There is no smoke without fire

Where they did they go yesterday.