Correct Answer: deadly

Solution : The correct choice is the first option .

Mortal often refers to something that is subject to death or capable of causing death. Deadly is the closest in meaning, as it describes something that can cause death or is extremely dangerous.

The meanings of other options are as follows:

• Benign implies harmlessness.
• Gentle suggests mildness or kindness.
• Lively refers to energetic or vivacious qualities.