A sentence has been given with a blank to be filled with an appropriate word. Choose the correct alternative.
When there are negative and toxic thoughts __________ your mind, you can never think positively.

Correct option is C

The correct alternative to fill in the blank is (c) clouding.
The sentence talks about negative and toxic thoughts that can never allow a person to think positively. The word clouding means to obscure or make something difficult to perceive or understand, which fits perfectly in the given context.
Meanings of other words are as follows:
•  Plot- a plan made in secret by a group of people to do something illegal or harmful.
•  Shout- (of a person) utter a loud cry, typically as an expression of a strong emotion.
•  Persuade- induce (someone) to do something through reasoning or argument.