Many doctors have … to western countries for better opportunities.

Analyze the question The sentence is "Many doctors have ___ to western countries for better opportunities." We need a past participle that fits after "have" and is followed by "to."

Explain the concept Migrate, emigrate and immigrate are easy to mix up:

• Migrate: to move from one place or country to another to live or work. It is general and is often followed by "to."
• Emigrate: to leave your own country (emigrate from).
• Immigrate: to enter a new country to settle there permanently (immigrate into or to, with the focus on arriving).

Solution

• A. migrated: fits grammatically and in meaning. Doctors moved from Nigeria to western countries to work. "Migrated to" is a common collocation.
• B. travelled: grammatically fine, but it only means going on a journey. It does not carry the idea of relocating for better opportunities.
• C. immigrated: this is possible, but "immigrate" emphasizes arriving and settling in the new country, from the destination's point of view. Here the sentence describes doctors leaving their home country, so it is less suitable than "migrated."
• D. participant: a noun, so it is grammatically wrong.

The best answer is **A.

Tip Remember: Emigrate = Exit a country, Immigrate = Into a country. When the sentence only talks about moving to another place for better opportunities, migrated is the safest general word. In "best completes" questions, first eliminate wrong parts of speech (like D), then choose the word with the most precise meaning.