Don't be shocked when you hear this

After a lecture if a student asks you a question and you don't know the answer of the question what will be your response in that situation?

Select the most appropriate option to substitute the underlined segment in the given sentence. If no substitution is required, select No improvement. You will not learn cycling unless you don't try. (a) unless you didn't try (b) unless you try (c) until you don't try (d) until you are not trying