Select the option that can be used as a one-word substitute for the given group of words.
Certain to happen

Correct option is B

The correct one-word for the given group of words is (b) Inevitable.
Inevitable means something that is certain to happen and cannot be avoided.
Example: Death is inevitable.
Meanings of the given other options:
· (a) Ineffective: not producing the desired effect.
· (c) Unexpected: not anticipated.
· (d) Avoidable: able to be prevented or avoided.