2. Choose the correct form: gerund, gerund + preposition, preposition + gerund, and complete the sentences

1. The importance of mentioning the surface of the country is...
A. by mentioning
B. mentioning
C. on mentioning
D. after mentioning

The correct answer is B. mentioning.
In this sentence, the phrase "the importance of mentioning the surface of the country" requires the use of a gerund, which is a verb form ending in "-ing" that functions as a noun. The gerund form "mentioning" correctly conveys the intended meaning.

2. Seeing Highland Britain is worthwhile...
A. of seeing
B. seeing
C. in seeing
D. on seeing

The correct answer is B. seeing.
In this sentence, the phrase "Seeing Highland Britain" acts as the subject of the sentence and requires a gerund to express the action. The gerund form "seeing" is the correct choice to convey the meaning that experiencing or visiting Highland Britain is worthwhile.

3. The UK continues...
A. with succeeding
B. succeeding with
C. in succeeding
D. succeeding in

The correct answer is C. in succeeding.
The verb "succeed" in this context requires the preposition "in" to indicate the area or domain in which the UK is succeeding. Therefore, the correct form is "succeeding in."

4. The UK succeeds in remaining...
A. remaining
B. in remaining
C. on remaining
D. remaining in

The correct answer is A. remaining.
The verb "succeed" in this sentence is followed by the preposition "in" to indicate the result or outcome of the success. The correct form is "succeeds in remaining," without the preposition "in" before "remaining."

5. The English...

Unfortunately, the sentence is incomplete, so it is not possible to provide a correct answer without the complete sentence. Please provide the complete sentence for further assistance.