## Core Concept
The strength of sewage refers to the measure of its organic content, which indicates the amount of oxygen required to break down the organic matter present. This concept is crucial in wastewater treatment and environmental engineering.

## Why the Correct Answer is Right
The correct answer, , is related to the measurement of sewage strength. Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are commonly used parameters. Total Dissolved Solids (TDS) and pH can also provide insights into sewage characteristics. However, is not a standard parameter for assessing sewage strength directly.

## Why Each Wrong Option is Incorrect
- **Option A:** BOD is a measure of the oxygen required to break down organic matter by microorganisms over a specific period, usually 5 days at 20°C. It is a direct indicator of sewage strength.
- **Option B:** COD measures the total amount of oxygen required to break down organic matter chemically. It provides a quicker assessment than BOD but is also indicative of sewage strength.
- **Option D:** TDS can indicate the overall dissolved content in sewage, which correlates with its strength.

## Clinical Pearl / High-Yield Fact
A key point to remember is that BOD5 (5-day BOD) and COD are critical parameters in assessing the strength of sewage. These values help in designing and operating wastewater treatment plants.

## Correct Answer: D.