The hobbyist could select any of the following plant combinations EXCEPT

The 4th rule states that if K is selected, X must also be selected. In the last question, you came to the conclusion that B was the answer because if there is no X, then there can't be K. The rule only states that if K is selected, X must be selected. It says nothing about what is required if X is selected. So why do we assume x cant be by itself with other variables?