Which of the following statements expresses the author's strongest certainty about his claim?
A、Prevalence of mixed depression, a combination of depression and manic or hypomanic symptoms, can be high in patients with bipolar disorders.
B、Prevalence of mixed depression, a combination of depression and manic or hypomanic symptoms, may be high in patients with bipolar disorders.
C、Prevalence of mixed depression, a combination of depression and manic or hypomanic symptoms, is high in patients with bipolar disorders.
D、Prevalence of mixed depression, a combination of depression and manic or hypomanic symptoms, might be high in patients with bipolar disorders.