Final answer:
Most of the sentences given are in the correct tense, indicating actions or situations in the past. However, Sentence 1 might be improved by using the simple present or past tense, as the current use of present continuous tense implies ongoing action, which may not be the intended meaning.
Step-by-step explanation:
The sentences you submitted are mostly in correct tense. The verb tenses used in the sentences align with the context of the action. Here are some general guidelines to assist you in understanding verb tenses in a sentence.
Past tense is used to represent an action or situation that occurred and finished in the past. Sentences 2, 4, 5, 6, 7, and 8 fit well in this category. For instance, in sentence 2 'He had just left the room when his mother arrived.', 'had left' is in past perfect tense whereas 'arrived' is in simple past tense. Both these tenses are correctly used here.
The present tense is used for actions taking place now or regularity. Sentence 1 appears to be an incorrect use of the present continuous tense. 'They have been arriving in this city' implies the action is ongoing which might not be the intention. It might be better to use simple present or past, i.e., 'They arrive in this city' or 'They arrived in this city'.
Present perfect tense is used for actions that have relevance to the current time or have just completed. And past continuous tense is often used for actions in the past that were incomplete when another action occurred. Sentence 3, 'They were returning when I reached home' is a correct usage of past continuous tense.
Learn more about Verb Tenses