This question tests your understanding of passive voice with infinitives in English grammar. The key concept here is how to correctly report past actions in passive constructions.

The original sentence "Many people think that the Vikings sailed to Canada" is in the active voice. When we transform this into a passive construction that starts with "The Vikings are thought...", we need to use an infinitive to complete the idea of what they are thought to have done.

Since the action of sailing (the verb "sail") happened in the past (the Vikings did it long ago), we must use the perfect infinitive to show that this action occurred before the time of the current belief. The perfect infinitive is formed with "to have" + the past participle of the main verb.

Let's break down the correct structure:

Subject (The Vikings) + Passive Verb (are thought) + Perfect Infinitive (to have sailed)

The verb "sail" is regular, so its past participle is "sailed". Therefore, the correct phrase is to have sailed.

Now, let's evaluate the options:

• to have been saled: Incorrect. "Saled" is not a word; the past participle of "sail" is "sailed".
• to sail: Incorrect. This is the present infinitive, which would imply the action is happening in the present or future, not the past.
• to be selling: Incorrect. This changes the verb to "sell", which has a completely different meaning and is grammatically wrong in this context.
• to have sailed: Correct. This is the perfect infinitive, correctly showing that the past action of sailing is what people think.

Final Answer: The Vikings are thought to have sailed to Canada.

Related Topics & Formulae

Passive Voice with Infinitives: This structure is commonly used with reporting verbs like think, believe, say, know, consider, etc. The general formula is:

Subject + passive reporting verb (e.g., is thought) + infinitive

The choice of infinitive depends on the timing of the action:

• Present Infinitive (to + base verb): Used for actions happening at the same time as the main verb.
  Example: She is known to be a great singer. (She is a great singer now.)
• Perfect Infinitive (to have + past participle): Used for actions that happened before the main verb.
  Example: He is believed to have left the country. (He left the country before now.)
• Continuous Infinitive (to be + present participle): Used for ongoing actions.
  Example: They are thought to be hiding in the forest. (The hiding is ongoing.)