Correct Answer: Harmful

Solution : The correct choice is the fourth option.

Insidious means proceeding in a gradual, subtle way with harmful effects and harmful directly conveys the idea of causing harm.

The meanings of the other options are as follows:

• Protected: It means kept safe or shielded from harm.

• Secure: It means free from danger or threat, often implying a sense of safety.

• Safe: It means free from harm or danger.