English

The idiom "As the crow flies" means the shortest distance between two points, or in a direct and straight way, without considering any obstacles or detours.

The correct preposition to use with 'co-operated' when referring to working jointly with someone is 'with'. Hence, 'The staff co-operated with the management' is correct.

The idiom "red letter day" refers to a day that is very important or memorable, often marked on calendars in red to signify its significance. Therefore, option B, "an important day," is the correct meaning.

The phrase 'darning the old socks' is the correct idiomatic expression referring to mending socks by sewing over holes. 'Darning' specifically means repairing fabric by weaving thread over the damaged area, which fits the context better than 'sewing' or 'stitching'.

The idiom "turned a deaf ear to" means to ignore or refuse to listen to someone or something, which matches option C exactly.

The idiom "leave someone in the lurch" means to abandon someone in a difficult or challenging situation without help. Therefore, option C, "To leave someone in difficulty," is the correct meaning.

The idiom "get the sack" means to be dismissed or fired from a job. Option D correctly captures this meaning, while the other options are either incorrect or less precise.

The word "populous" means having a large population or being densely populated. Among the options, "heaving" can mean crowded or full of people, which is closest in meaning to "populous." The other options do not relate to population density.

The preposition 'during' correctly indicates the time period in which the rapid development occurred, making it the appropriate choice for the sentence.

Option C, "They should shoot the traitors dead," correctly uses the modal verb "should" followed by the base verb "shoot," which is the proper structure for expressing obligation or recommendation in active voice. The original sentence is passive, and option C is the correct active voice equivalent.