Fill in the blanks:
a. A cuboid is also known as a rectangular.....
b. The face on which a solid rests is called the.....of the solid.

Answer

To solve the problem, we need to fill in the blanks with the correct terms related to three-dimensional shapes.

### Step-by-Step Solution:

1. **Understanding the First Blank**:
- A cuboid is a three-dimensional shape with six rectangular faces. It is often referred to in geometry as a rectangular prism.
- Therefore, the first blank can be filled with "prism".

**First Blank Answer**: A cuboid is also known as a rectangular **prism**.

2. **Understanding the Second Blank**:
- The term used for the face on which a solid rests is commonly referred to as the "base". This is because the base is the surface that supports the solid.
- Hence, the second blank can be filled with "base".

**Second Blank Answer**: The face on which a solid rests is called the **base** of the solid.

### Final Answers:
a. A cuboid is also known as a rectangular **prism**.
b. The face on which a solid rests is called the **base** of the solid.