I. Conformers are the organisms that cannot maintain a constant internal environment.
II. 99% animals and nearly all plants cannot maintain their constant internal environments
III. During the course of evolution, the cost and benefits of maintaining a constant internal environment are discarded.
IV. Conformity is a condition in which an external challenge induces parallel internal changes.
V. Regulation is a condition in which external challenge elicits compensatory action to maintain the internal environment.

Options

A. All are correct
B. All are wrong
C. Only Ill is wrong
D. Only IV and V are wrong

Answer

To solve the question regarding the correctness of the five statements about conformers and regulators, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I**: "Conformers are the organisms that cannot maintain a constant internal environment."
- **Analysis**: This statement is correct. Conformers are organisms that adjust their internal environment according to external conditions. They do not have mechanisms to regulate their internal environment independently of external changes.

2. **Statement II**: "99% animals and nearly all plants cannot maintain their constant internal environments."
- **Analysis**: This statement is also correct. Most animals (about 99%) and nearly all plants are conformers, meaning they cannot maintain a stable internal environment regardless of external conditions.

3. **Statement III**: "During the course of evolution, the cost and benefits of maintaining a constant internal environment are discarded."
- **Analysis**: This statement is incorrect. Maintaining a constant internal environment (homeostasis) is crucial for the survival and efficiency of many species, particularly endothermic animals (like mammals). Evolution has favored those organisms that can maintain homeostasis, not discarded it.

4. **Statement IV**: "Conformity is a condition in which an external challenge induces parallel internal changes."
- **Analysis**: This statement is correct. Conformity refers to the phenomenon where an organism's internal conditions change in response to external environmental changes.

5. **Statement V**: "Regulation is a condition in which external challenge elicits compensatory action to maintain the internal environment."
- **Analysis**: This statement is correct. Regulation involves mechanisms that organisms use to maintain a stable internal environment despite changes in external conditions.

### Conclusion:
- From the analysis, we can conclude:
- Statements I, II, IV, and V are correct.
- Statement III is incorrect.

### Final Answer:
- The correct option is **Option 3: only statement III is wrong**.