First, use the exclusion method.

The total number of any three is (three tenths) 10C3= 120 species.

Excluding C, select 120-9C2=84 (determine C, and select 2 of the remaining 9).

Then remove the ones that A and B didn't choose (excluding A and B, leaving eight to choose three) 84-8C3=28 kinds.

Because C was selected, A and B were not selected, so I calculated it again (excluding A and B, determining C and taking two of the remaining seven), so I added it.

28+7C2=49 species

So, the answer is 49

Second, use addition principle.

If c is not selected, it can be removed directly, leaving 9 people.

That is, select A, deselect B (exclude B, confirm A, and select two of the remaining seven) plus select B, deselect A (exclude A, confirm B, and select two of the remaining seven) plus select both parties (confirm A and B, and select one of the remaining seven).

7C2+7C2+7C 1=49 species.

Make sure there is only one in the combination.

Personally, I prefer xenophobia.