Voice expressions can effectively be judged by

The correct answer is tone of voice.

Step-by-step Explanation:

1. Understanding Voice Expressions: Voice expressions, or vocalics (paralanguage), refer to the non-verbal cues of the voice that convey emotions, attitudes, and meaning alongside or independent of the spoken words.
2. Analyzing the Options:
- Words selection: This refers to verbal communication (what is said) rather than vocal expression (how it is said).
- Tone of voice: This represents the quality, pitch, modulation, and emotional color of the voice. It directly reflects a speaker's feelings (e.g., excitement, anger, sarcasm, or warmth) and is the primary channel through which voice expressions are judged.
- Vocals: This is a broad term that can refer to singing or general sound production, which is less specific than tone for judging expressions.
- Speed of voice: While speed (tempo) is a vocal cue that can indicate nervousness or excitement, it is only one component of paralanguage and is less comprehensive than the overall tone of voice for judging emotional expression.
3. Conclusion: Therefore, the tone of voice is the most effective and primary indicator used to judge vocal expressions and emotional undertones in communication.