なぜこの文脈では不定冠詞を使うのでしょうかの英語

I don't really understand how to use prepositions.

the prepositional phrase here is used adverbially

You can omit the preposition in this phrase.

The following verbs only take the to-infinitive as their object.

It is difficult to use the prepositions properly.

This sentence is in the present perfect. 'have' is not a verb, but an auxiliary verb.

The verb 'help' takes to-infinitives and bare infinitives but bare infinitives are said to be the most common in casual text; as also used in this example sentence.

In English, the use of prepositions is hard to learn.

Why does English have so many idioms and phrasal verbs?

In a progressive tense sentence it becomes the -ing form verb, that is the present participle.

In English the verb precedes the object.

The next sentence has adjectives and adverbs.

It is difficult to use prepositions correctly.

This type of noun phrase is called a "concealed question".

a pronoun (as `that' or `which' or `who') that introduces a relative clause referring to some antecedent

A sentence normally has a subject and a verb.

of or relating to or formed with a preposition

an interrogative adverb

an infinitive with an adverb between `to' and the verb (e.g., `to boldly go')

Put the verbs in the present perfect.

in English the subject and the verb must agree in number

Relative pronouns perform as 'conjunction + pronoun'.

Can you conjugate this verb?

Sometimes a verb is derived from a noun and sometimes it is the other way around.

I'm teaching basic participial constructions now, but, with regard to those below, what different ways of translating them would everybody use?

a word to express something in an indirect way

This verb is normally used only in the third person.

I'd like to ask a grammarian, isn't it possible to think of 'be + participle' like you do V C and such?

causal conjunctions

an interrogative pronoun