When a Group of Students Was Told by Its Mentors

When a group of students was told by its mentors that intelligence was changeable and could be improved,

A) they later scored no better than a control group on math tests but showed minor increases in tests of comprehension.
B) they later scored much higher on math tests than did a control group, and this was particularly true for girls.
C) the girls improved significantly, but the boys did not, compared with a control group.
D) the boys improved significantly, but the girls did not.