English

The word 'fickle' means changing frequently, especially in loyalty or affection. Its antonym is 'constant,' which means unchanging or steady, making option C the correct answer.

The word 'astound' means to amaze or greatly surprise someone, which matches option A. The other options do not relate to the meaning of 'astound'.

The word "pit" refers to a hole or a low point, so its antonym is "peak," which means the highest point or summit. The other options do not represent opposites of "pit."

The word 'revealed' means made known or disclosed. Its antonym is 'concealed,' which means kept hidden or secret. The other options do not directly oppose the meaning of 'revealed.'

The sentence is a negative question tag referring to a past action completed before a specific time, so the correct tag is 'didn't you?' because the main clause is in the past simple tense.

The phrase 'put off' means to postpone or delay something, which fits the context of the meeting being delayed because the chairman was out of the country. The other options do not convey this meaning correctly.

The word 'kindle' means to start a fire or ignite. The antonym is 'douse,' which means to extinguish or put out a fire, making option B the correct answer.

The phrase "willy-nilly" means doing something in a haphazard or unplanned manner, which matches option B. The other options do not convey this meaning.

The English language is estimated to have approximately 250,000 to 300,000 words in current use, making option B (250,000) the closest and most accurate choice among the given options.

The word 'trammel' means a restriction or obstacle that prevents free action, so 'Obstacle' is the correct synonym among the options provided.