First of all, you must understand what ing is. There are two forms of ing. One is called a gerund, which functions as a noun and serves as the subject, object, predicate, and attributive in the sentence
The other is called the present participle, which functions as an adjective and usually has three meanings. 1.
Indicates a (person or thing) that makes people...
2.
Indicates ongoing actions
3. Indicates active actions,
can serve as attributive, predicate, adverbial, and object complement in a sentence
There are three changes in your question ing
The first one, the second line, how
to
improving, this change is wrong, sentence In the middle how
to
the verb base form is the verb infinitive with a special question word as the object in the sentence, so the improve base form should be used
The second part , C
The last line of the essay, look
forward
In the phrasal verb to, to is a preposition, and the preposition is followed by a noun, a pronoun, and a gerund ( i.e. ing), so ing should be added to the following hear
In the third place, in the first line of the passage D, come needs to use coming, because the preceding was is followed by the present participle (i.e. ing) to form a verb past continuous tense. Indicates ongoing action.