If so, the answer is D.

Can be explained by classification. According to the order of six days and two days, the number of people can be 0 or 4. 1、3; 2、2; 3、 1; 4, 0 cases, of which 1, 3 has four possibilities, 2, 2 has six possibilities, 3, 1 has four possibilities, so there are1+4+6+4+1=16 possibilities in total, and two.

(This is the way of thinking in junior high school)