Characteristics of bipolar disorder typically include
a. hypochondria.
b. difficulty concentrating.
c. attacks of amnesia.
d. manipulation of others

The correct answer is option b, that is, difficulty concentrating.  

Manic depression also called bipolar disorder refers to a mental disorder, which leads to periods of unusually elevated mood and the periods of depression. The elevated mood is substantial and is called hypomania or mania, on the basis of its severity, or whether the signs of psychosis are there.  

One of the usual sign of bipolar disorder is the difficulty in concentrating or diminished the tendency to think and indecisiveness. The individual suffering with the condition seems to make wrong decisions due to this sign, and as they do not think completely, the patients suffering from bipolar disorder possess poor decision making.