A scientist tests the null hypothesis that the mean height of plants in their population is 0.75 meters, as it is in a nearby population observed with a complete census of all plants. Assume that this null hypothesis is true.

However, the plants in his sample were chosen non-randomly, and the tallest plants were more likely to be chosen than expected by chance.

Which of the following statements is true?

a. A hypothesis test based on this biased sample would have an increased probability of making a Type I error.

b. This sampling bias will not affect the probability of a Type I error.