Though vertebrates are aerobes, but their `ul((i))` show anaerobic respiration during `ul((iii))`. During this `ul((iii))` of skeletal muscle fibres is broken down to release lactic acid and energy. Lactic acid, if accumulates causes muscle fatigue. Fill up the blanks in the above paragraph and select the correct option.

Options

A. `{:((i),(ii),(iii).),("skeletal muscles","heavy exercise","glucose"):}`
B. `{:((i),(ii),(iii).),("skeletal muscles","mild exercise","glycogen"):}`
C. `{:((i),(ii),(iii).),("skeletal muscles","heavy exercise","glycogen"):}`
D. `{:((i),(ii),(iii).),("cardiac muscles","heavy exercise","glycogen"):}`

Explanation

To fill in the blanks in the provided paragraph, we need to identify the correct terms based on the context of respiration in vertebrates, particularly during strenuous exercise. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Identify the Type of Organism**:
- The paragraph begins by stating that vertebrates are aerobes. This means they primarily rely on aerobic respiration for energy production.

2. **Identify the Specific Muscles Involved**:
- The first blank refers to what part of the vertebrates shows anaerobic respiration. During strenuous exercise, it is the **skeletal muscles** that undergo anaerobic respiration due to a lack of oxygen.

3. **Identify the Condition Under Which Anaerobic Respiration Occurs**:
- The second blank refers to the condition or activity that leads to anaerobic respiration. This occurs during **heavy exercise** when the demand for oxygen exceeds the supply.

4. **Identify the Substrate Being Broken Down**:
- The third blank refers to what is being broken down in the skeletal muscle fibers. During anaerobic respiration, **glucose** is broken down to produce lactic acid and energy.

5. **Summarize the Completed Paragraph**:
- The completed paragraph reads: "Though vertebrates are aerobes, their **skeletal muscles** show anaerobic respiration during **heavy exercise**. During this **glucose** of the skeletal muscle fibers is broken down to release lactic acid and energy. Lactic acid, if accumulates causes muscle fatigue."

### Final Answer:
- 1st Blank: **skeletal muscles**
- 2nd Blank: **heavy exercise**
- 3rd Blank: **glucose**