This question tests your understanding of reduced relative clauses using infinitives. The original sentence is: "The last one who was caught was a bank robber." We need to transform the relative clause ("who was caught") into an infinitive phrase to fill in the blank.

Let's break down the original clause:

• "who was caught" is a passive voice construction. The subject ("who") is the receiver of the action (being caught).

When we reduce a relative clause that is in the passive voice to an infinitive phrase, the correct form is "to be + past participle".

Therefore, the clause "who was caught" becomes "to be caught".

The complete transformed sentence is: The last one to be caught was a bank robber.

Let's see why the other options are incorrect:

• to catch: This is active voice ("to do the catching"). It would imply the "last one" is the person doing the catching, not the one being caught.
• to have been caught: This uses the perfect infinitive ("to have been"), which is used for an action that was completed before the time of the main verb. The simple infinitive "to be" is sufficient here to describe a general state.
• to be catching: This is the continuous active form ("to be in the process of catching"), which again incorrectly describes the "last one" as the person performing the action.

Related Topic & Formula

Topic: Reduced Relative Clauses with Infinitives

Rule/Formula:

To reduce a relative clause in the passive voice, you can often replace it with an infinitive phrase. The structure is:

$\mathrm{to\; be}+\text{past participle}$

Example: "He was the first player who was selected for the team." becomes "He was the first player to be selected for the team."