Concept:“A wet blanket” is an idiom for someone who spoils or dampens other people’s fun.Explanation:The phrase “a wet blanket” does not mean getting physically wet or being disloyal.It describes a person who is negative, disapproving, or unwilling to join in.Such a person makes others feel less cheerful or enthusiastic.Therefore, Helen’s behaviour makes others unable to enjoy themselves fully.Answer:D. stops others from enjoying themselves.