If More Than Half of Patients with Depression Show Improvement

If more than half of patients with depression show improvement after six months of therapy,what conclusion,if any,can we draw? If none,why not?​

A) We conclude that the therapy was effective for most of the patients.
B) ​We conclude that the therapy was effective for some of the patients.
C) ​We draw no conclusion, because patients with depression are different from other people.
D) ​We draw no conclusion, because the study had no control group.