单选题 The major difference between bipolar Ⅰ and bipolar Ⅱ disorder is that
A．Clients with bipolar Ⅰ have no symptoms of mania, but only depression
B．The prognosis for bipolar Ⅰ is much better than for bipolar Ⅱ
C．Both disorders are the same, except that clients with bipolar Ⅰ disorders have a much higher incidence of suicide
D．Clients with bipolar Ⅱ disorder do not have symptoms of mania that interfere enough to cause marked functional disturbances