1. The set of 6-letter strings that contain at most one type of vowel—multiple uses of the same vowel are fine, but no two different vowels can appear. (So BANANA, RHYTHM, and BOOBOO are fine; ESCAPE...

1. The set of 6-letter strings that contain at most one type of vowel—multiple uses of the same vowel are fine, but no two different vowels can appear. (So BANANA, RHYTHM, and BOOBOO are fine; ESCAPE and STRAIN are not.)

2.