Choose the correct verb form from those in brackets.

The earth _ round the sun.

The given sentence is grammatically correct and there is no error.

The error is in first part. ‘One of the’ should always be followed by a plural noun, expressing that the speaker chooses one from many. Hence ‘features of travel’ is the correct expression, indicating that there are many interesting features about Himachal Pradesh but the most interesting one among them is the provision of large number of travelers’ lodges.

The error is in third part. By using ‘not’ after ‘unless’, both the negatives cancel each other. So, the correct usage will be ‘unless he reports for duty immediately’. Since “unless” is negative it should be
followed by affirmation, like “unless he reports for duty”. Incase “unless” was absent, we could have written “if he does not report” and expressed the same meaning.

The error is in first part. ‘Considering’ is a preposition that relates the facts to the principal and hence does not need to be followed by another preposition ‘about’. A preposition like ‘considering’ should be followed by a pronoun like ‘these’ in this case. The use of about is unnecessary and shall be omitted. The sentence indicates that the principal offered him a seat only after considering certain facts.

Error is in third part. Here, “there” is an adverb that qualifies the verb ‘is’. The position of ‘there’ in the sentence is incorrect. The correct usage should be ‘there is no trouble’. It indicates the absence of any trouble in a country.

Error is in second part. Returning means coming back to place from where you began. So, the use of back after returned becomes redundant. Without using back, the meaning remains the same. We can omit ‘back’ in part b, and use ‘returned home.’

Error is in third part. Since “doing” was used in second part it should be followed by “doing” in third part as well instead of using “done”. Such repetitive figure of speech is used in
English grammar to create emphasis. This sentence indicates that a thing that is worth doing is also worthy of doing well. Here worth is the noun that must be followed by the verb doing.

The error is in second part. In the given sentence two events occur one after the other. ‘He left’ before ‘we reached’. So, the event that was completed before the occurrence of the next event shall be expressed in past perfect tense. Therefore, the correct form of verb will be “had left”.