Answer and Explanation:
1. B: Its is incorrect because it is a determiner; the correct is to use the contracted form of <em>it is </em>: it's. <em>It's going to be difficult to prepare</em>.
2. B: Who is incorrect because the preposition from requires an object, and the appropriate pronoun is whom . <em>From whom should...?</em>
3. D: Their is a determiner, but the correct is the contracted form of <em>they are </em>: they're. <em>They're getting into lots of mischief</em>.
4. B: <em>present Progressive </em>: is listening is an action in progress in the present. It is present progressive (or continuous) tense.
5. C: <em>Past:</em> Left is the past of the verb <em>leave </em>. Simple Past tense.
6. D: <em>Past Perfect : </em>The action "He had thought" happened before the action "it was".
7. C: Most famous. This the superlative for the adjective <em>famous: The most famous</em>
8. C: Busiest. The adjective <em>busy </em> is short, and its superlative is formed by replacing y by i, and adding est: <em>the busiest</em>
