Final answer:
12. "Was" is a helping verb that helps to form the past continuous tense. 13. In this sentence, the word "staring" is a gerund. 20. In this sentence, "flying" is classified as a present participle.
Step-by-step explanation:
12. "Was" is a helping verb that helps to form the past continuous tense. In this sentence, it is helping to show the action of staring happening in the past. Helping verbs work with main verbs to express various tenses and moods in a sentence.
13. In this sentence, the word "staring" is a gerund. A gerund is a verb form that functions as a noun. In this case, it is the subject of the sentence. Even if you can't find a subject in a sentence, it can still be a complete sentence if it has a verb and expresses a complete thought.
20. In this sentence, "flying" is classified as a present participle. It is functioning as part of a compound verb. A present participle is a verb form ending in -ing that functions as an adjective or as part of a verb phrase.