The infinitive is the base form of a verb. It is often preceded by the word to. Infinitives often appear after other verbs. Some verbs have an object before the infinitive. In these examples, the objects are in bold.

We form the past perfect with had + past participle. We use the past perfect for a past action which happened before another past action.

The indefinite articles a and an are used before singular countable nouns. The is a definite article.

Verb tenses tell you when an action happens. If the action happens regularly, sometimes or never, we use the simple present tense. The simple present tense is also used to state facts.

Conditionals consist of the if-clause (guess), which begins with the word if, and the main clause, which shows the result of the guess.

What is the difference between a sentence and a phrase? What is a noun phrase? What is an adjective phrase? What is an adverb phrase?

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The highlighted words below (was built, is visited, etc.) are examples of the passive. We use the passive if we do not know who does something, or if it is not important or not necessary to say who does it.