Only depress the central nervous system. This is the only choice that’s actually a statement, so it should be pretty easy to pick the right answer. “N,” “N,” and “N” are not plausible statements about psychoactive drugs. They are neither true nor false.
The correct answer is option C, because the word ‘only’ makes it false. While it’s true that some psychoactive drugs have a depressant effect on the central nervous system, others are stimulants, hallucinogens, or have other kinds of effects on the brain.
Option C describes one subcategory of psychoactive drugs, not the whole group of psychoactive drugs itself. Depressants are frequently used as sleeping pills (e.g. Seconal and other barbiturates), whereas others are used as anti-anxiety medication (e.g. Xanax).