Feelings of sadness:
A) Sadness can occur within anybody, not just a symptom of depression. This option is out of the question, since it is wrong.
B) Feelings of sadness are usually linked to depression when felt over a long period of time. Studies say that sadness is only a little part of depression, while you mostly feel rejected, hopeless, and worthless. Looking at the other options, this would be the most reasonable answer.
C) This CAN be true in some ways, but panic attacks can be triggered by so many things. The #1 reason is usually when you're nervous or anxious. Panic attacks can even happen out of the blue. Sadness can lead to panic attacks, but not usually. I would say no for this option.
D) Sadness should NOT be ignored when they last over a long period of time. If you are sad for a certain time period, you should look into talking to somebody about the issue. This option is obviously false.
Out of the choices, two out of four were reasonable, but I would have to go with B) are one of the major symptoms of depression.