@Christian,
I'm afraid you do not understand the concepts of "multichoice" and "multianswer".
A multichoice question presents the student with a choice of at least 2 answers. You cannot have a multichoice question with only one answer, it's illogical.
Q1.- Which one is an animal?
- the cat (correct choice)
- the rose (incorrect choice)
- the bus(incorrect choice)
If you want to ask a multichoice question where more than one choice is "correct", than you check the multianswer box.
Q2. Which of these animals are mammals?
- the cat (correct)
- the whale (correct)
- the trout (incorrect)
- the butterfly(incorrect)
Hope that helps,
Joseph