In the if-clauseA group of related words containing a subject and a verb. of the first conditional we can use should (to express that the condition is less likely), can (permission or ability), will or would (willingness, insistence and refusal), must (obligation) or may (permission).

If superlative adjectiveA part of speech that modifies, qualifies or restricts a noun or a pronoun. E.g.: The apples are ripe. ("ripe")s (especially the first, the last) are used, an infinitive structureThe way in which the parts of a sentence, clause or expression are arranged. E.g.: make somebody + infinitive in "The teacher made me rewrite the composition." can replace a defining relative clauseA group of related words containing a subject and a verb..

Geoffrey was the last to understand the joke. (= Geoffrey was the last person who understood the joke.)

If we want to express an actionA general term expressing that somebody or something does something in the passive voiceThe form of the transitive verb that shows whether the subject acts (active voice) or is acted upon (passive voice)., a passive infinitive is used:

In time clauseA group of related words containing a subject and a verb.s that refer to future time (for example clauses with after, as soon as, until, when, while etc.) we use present tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses.s.