Do psychiatrists normally perform physiological tests (e. g., blood work, brain scans) to diagnose mental illnesses?

Not always.

Explanation:

I myself have been through many physiological tests. They do blood work, ekg scans, vital checks, and so on. They only do brain scans if they believe that one NEEDS to be done.

i am positive it is c. condensing but i may be wrong

the answer to your question is:

c. complementary base-pairing