Step 1: Understanding the Concept:
Communication is categorized into verbal (using words) and non-verbal (without words).
Non-verbal communication involves body language, facial expressions, and gestures.
Step 2: Detailed Explanation:
(A) Sending a text message: This uses written words, making it verbal communication.
(B) Speaking loudly: This is verbal as it involves speech, though the volume is a para-verbal cue.
(C) Maintaining eye contact: This is a form of body language that conveys message and intent without using any spoken or written words.
(D) Writing an email: This is a form of written verbal communication.
Step 3: Final Answer:
Since eye contact involves conveying information through physical behavior rather than language, option (C) is the correct answer.