Is this a Sentence or fragment

That book is heavy.

Which line in the passage can be used as textual evidence to support the following claim? many people suffer from depression. depression is a serious mental illness that affects a person physically and mentally. it interferes with a person's ability to function normally and enjoy pleasurable activities. some types of depression include major depressive disorder, seasonal affective disorder, and postpartum depression. many people confuse depression with general sadness, though people are becoming increasingly aware that it is indeed a serious illness. often people suffering from depression think that it is an incurable condition. they don’t seek any treatment because they are afraid of how others will judge them. based on data from the national institute of medical health, depressive disorders are common and affect 9.5 percent of adults in the united states, or about 19 million people every year. more than 80 percent of people with depressive disorders improve when they receive appropriate treatment.