Which of the following is a sign of depressant influence?

Thick, slurred speech is a common sign of depressant influence on the central nervous system. Depressants, which include substances like alcohol and certain medications, work by slowing down brain activity. This can lead to a reduction in motor function and coordination, affecting the clarity and fluidity of speech. As a result, individuals under the influence of depressants may have difficulty articulating words clearly, leading to slurred speech.

In contrast, increased alertness, euphoria, and excitation are typically associated with stimulant substances, which act to enhance brain activity and can result in heightened energy levels, mood elevation, and increased responsiveness. Therefore, thick, slurred speech serves as a clear indicator of depressant influence, making it the correct choice.