What is the scientific explaination for the feeling of depression ?

Question

$\begin{array}{1 1} \text{(a) A person suffers from depression when he has low levels of blood pressure .} \\ \text{(b) A person suffers from depression when he has low levels of norepinephrine .} \\ \text {(c) A person suffers from depression when he has high levels of norepinephrine .} \\(d)\;\text{A person suffers from depression when he has low levels of sugar } \end{array}$