First let's find the total number of students:
[tex]S=20+33+26=79[/tex]Now, let's divide this total by 6, 7, 8, 9 and 10, and check if the result has no remaining (that is, the result is a whole number):
[tex]\begin{gathered} \frac{79}{6}=13.167 \\ \\ \frac{79}{7}=11.286 \\ \\ \frac{79}{8}=9.875 \\ \\ \frac{79}{9}=8.778 \\ \\ \frac{79}{10}=7.9 \end{gathered}[/tex]Since none of the results is a whole number, it's impossible to divide these students in teams with the same number of students.
Therefore the correct option is the second one.