Mark the correct statement

Options

A. All mammals have placenta
B. All chondrichthyes are marine animals with a streamlined body with some exceptions
C. Larve of all cyclostomates return to fresh water after metamorphosis
D. Choline and Testudo are able to maintain a constant body temperature

Answer

To solve the question, we need to evaluate each of the four statements provided and determine which one is correct.

### Step-by-Step Solution:

1. **Evaluate Statement 1: "All mammals have placenta."**
- The placenta is an organ that develops during pregnancy to provide nutrients and oxygen to the fetus while removing waste.
- However, not all mammals have a placenta. For example, marsupials (like kangaroos) carry their young in pouches and monotremes (like the platypus) lay eggs.
- **Conclusion:** This statement is **incorrect**.

2. **Evaluate Statement 2: "All Chondrichthyes are marine with streamlined body with some exceptions."**
- Chondrichthyes are a class of fishes that have a cartilaginous skeleton. They are primarily marine and typically have streamlined bodies.
- There are indeed some exceptions to this generalization, but the statement acknowledges that there are exceptions.
- **Conclusion:** This statement is **correct**.

3. **Evaluate Statement 3: "Larvae of all Cyclostomates return to fresh water after metamorphosis."**
- Cyclostomates are jawless fish, such as lampreys and hagfish. They are generally marine but migrate to freshwater to spawn.
- After spawning, their larvae do not return to freshwater; instead, they typically return to the marine environment.
- **Conclusion:** This statement is **incorrect**.

4. **Evaluate Statement 4: "Chillon and Testudo are able to maintain a constant body temperature."**
- Chillon refers to turtles and Testudo refers to tortoises, both of which belong to the class Reptilia.
- Reptiles are ectothermic (cold-blooded) and do not have the ability to maintain a constant body temperature internally.
- **Conclusion:** This statement is **incorrect**.

### Final Conclusion:
After evaluating all four statements, the correct statement is **Statement 2: "All Chondrichthyes are marine with streamlined body with some exceptions."**