Correct Answer: (a) have no doubt that there is a lesson
Solution:We generally use a singular verb with a singular subject. But, 'I' is an exception. The pronoun 'I' is singular but always takes a plural verb in the present tense. For eg- I have a good boy Vishal who helps me. Similarly, in the given sentence, we will use a plural verb (have). Hence, 'I have no doubt that there is a lesson' becomes the most appropriate answer.