An open-ended question is that could be used to start a discussion, 'Why do you think the bus should run more often?' is an open-ended question.
Answer: B
Explanation
A question which does not have an answer as 'yes' or 'no' are open-ended questions.
They are questions where the answers are expected to be more than a single word.
To start a group-discussion or conversation, these questions play a vital role in bringing opinions of everyone participating in the discussion or conversation.
The rest questions mentioned above have answers only as 'yes' or 'no'.