One, invite A instead of B, then choose 5 students from 8 students, that is, 5 ***56 kinds of footprints under C and 8 kinds above C.

Second, invite B to invite A, but choose 5 from 8 students, that is, 5 ***56 kinds of footprints under C and 8 kinds above C.

Third, if there is no A and no B, then six out of eight students will be selected, that is, six kinds of footprints under C, eight kinds of footprints above C and 28 kinds of footprints.

Add up to 56+56+28 = 140 species.

Or subtract all cases in which Party A and Party B participate.

Party A and Party B participate together, that is, there are 70 kinds of footprints, 8 kinds of footprints and 4 kinds of footprints.

C bottom footer 10 top footer 6-70=2 10-70= 140.

The answer of the two methods is the same.