A bolus is

Options

A. a mass of crushed food moistened with saliva
B. the semisolid material resulting from partial digestion in the stomach
C. the milky emulfied fat absorbed from small intestine
D. indigestible materials that help in movement and absorption of food.

Explanation

### Step-by-Step Solution:

1. **Understanding the Term "Bolus":**
- A bolus refers to a mass of food that has been chewed and mixed with saliva in the mouth. This process makes the food easier to swallow and prepares it for digestion.

2. **Analyzing the Options:**
- **Option 1:** A mass of crushed food moistened with saliva.
- **Option 2:** Semi-solid material resulting from partial digestion in the stomach (this is called chyme).
- **Option 3:** Milky emulsified fat absorbed from the small intestine (this is called chyle).
- **Option 4:** Indigestible material that helps in the movement and absorption of food (this refers to dietary fiber).

3. **Identifying the Correct Definition:**
- The correct definition of a bolus aligns with Option 1, which describes it as a mass of crushed food moistened with saliva. This is the state of food before it enters the stomach.

4. **Conclusion:**
- Therefore, the correct answer to the question "A bolus is" is **Option 1: a mass of crushed food moistened with saliva**.