Explanation

The degree of saturation is defined as the ratio of the volume of water to the volume of voids in soil. The question describes the percentage of water volume relative to the total volume of solids, which actually defines the volumetric water content or moisture content by volume. However, in many simplified contexts, 'Degree of saturation' is often confused with this definition, but strictly speaking, it's the ratio of water volume to void volume. Wait, let me re-read carefully. 'percentage of the volume of water filled in voids to the total volume of solids'. This is actually Volumetric Water Content (theta) or Moisture Content by volume. None of the options perfectly match this standard definition except maybe a misinterpretation. Let's check standard definitions. Void ratio e = Vv/Vs. Degree of saturation S = Vw/Vv. The question asks for Vw/Vs. This is not S. However, in some older or less precise texts, there might be confusion. But strictly, the answer should be Volumetric Water Content. Since that's not an option, and 'Degree of saturation' is the closest related term often tested, but it's technically incorrect. Actually, looking at common MCQ banks for soil mechanics, this specific phrasing often appears with 'Degree of saturation' as the intended answer despite the technical inaccuracy regarding 'solids' vs 'voids', OR the question meant 'volume of voids'. If the question says 'filled in voids to total volume of solids', it's Vw/Vs. This is not S. However, if I must choose from options, C is the standard distractor/answer in many flawed banks. But wait, is there a term? No. I will mark needsReview true because the definition provided in the question (Vw/Vs) does not match Degree of Saturation (Vw/Vv). The correct term is Volumetric Water Content. Since it's missing, and C is technically wrong, I should flag this.