Bones of birds are

Options

A. Solid and heavy
B. Solid and light
C. Spongy and light
D. Spongy and heavy

Answer

To answer the question "Bones of birds are," we can follow these steps:

### Step 1: Understand the Structure of Bird Bones
Birds have a unique skeletal structure that is adapted for flight. Unlike mammals, their bones are not solid and heavy.

**Hint:** Consider how the structure of bones can affect an animal's ability to fly.

### Step 2: Identify the Characteristics of Bird Bones
Bird bones are known to be lighter in weight compared to the bones of mammals. This lightweight structure is crucial for flight, as it reduces the overall body weight of the bird.

**Hint:** Think about why lighter bones would be beneficial for an animal that flies.

### Step 3: Consider the Composition of Bird Bones
In addition to being light, many bird bones are also spongy. This spongy texture contributes to their lightweight nature and provides structural support without adding unnecessary weight.

**Hint:** Reflect on how spongy bones might provide strength while remaining light.

### Step 4: Recognize the Functionality of Bird Bones
Some bird bones are hollow, which not only contributes to their lightness but also plays a role in the avian respiratory system. The hollow spaces allow for air sacs that are part of the bird's breathing mechanism.

**Hint:** Think about how the respiratory system of birds is different from that of mammals.

### Step 5: Conclude the Answer
Based on the characteristics discussed, we can conclude that the bones of birds are "spongy and light."

**Final Answer:** Bones of birds are spongy and light.