Correct Answer: pollute

Solution : The third option is the correct answer.

The word contaminate means to make something impure or introduce pollutants, often leading to a decrease in quality or purity. Its synonym, pollute, shares a similar meaning, involving the introduction of harmful or undesirable elements that degrade the original state of something.

The meanings of the other options are as follows:

• Sanctify means to make holy or sacred.
• Purify means to remove impurities or pollutants.
• Cleanse also involves purifying or removing impurities.

Therefore, the correct answer is pollute.