______are used between surfaces where friction needs to be minimized, such as in machine parts.

Options

A. Gels
B. Lubricants
C. Water
D. None of them

Answer

To solve the question, we need to identify the substances that are specifically used to minimize friction between surfaces, particularly in machine parts. Here’s a step-by-step breakdown:

### Step 1: Understand the Question
The question asks for a specific type of substance that is used to reduce friction between surfaces, especially in machine parts.

**Hint:** Think about what substances are commonly applied to moving parts in machines to help them operate smoothly.

### Step 2: Identify the Options
Although the options are not provided in the question, we can infer that the answer will likely be a term related to reducing friction.

**Hint:** Consider common terms used in mechanics and engineering that relate to friction reduction.

### Step 3: Recall Relevant Terms
In mechanics, there are several terms related to reducing friction, such as "lubricants," "oils," "greases," etc. However, "lubricants" is the most general and widely used term.

**Hint:** Which of these substances is specifically designed to be applied to surfaces to minimize friction?

### Step 4: Conclude the Answer
Based on the understanding that lubricants are substances that reduce friction, we can conclude that the answer to the question is "Lubricants."

**Hint:** Remember that lubricants can come in various forms, such as oils or greases, and are essential in many mechanical applications.

### Final Answer
**Lubricants are used between surfaces where friction needs to be minimized, such as in machine parts.**