Which of the following is an oviparous mammal?

Options

A. Balaenoptera
B. Delphinus
C. Pteropus
D. Ornithorhynchus

Answer

To determine which of the following is an oviparous mammal, we need to analyze each option provided:

1. **Balenoptera**: This genus includes the blue whale and other large whales. Whales are known to be viviparous, meaning they give birth to live young. Therefore, this option is incorrect.

2. **Delphinus**: This refers to common dolphins. Like whales, dolphins are also viviparous and give birth to live young. Thus, this option is also incorrect.

3. **Pteropus**: Commonly known as fruit bats or flying foxes, these mammals are also viviparous, as they give birth to live young. Therefore, this option is incorrect as well.

4. **Ornithorhynchus**: This is commonly known as the platypus. The platypus is unique among mammals as it lays eggs, making it an oviparous mammal. Thus, this option is correct.

In conclusion, the correct answer is **Ornithorhynchus**.

### Summary of Steps:
1. Identify the nature of each option (oviparous or viviparous).
2. Analyze Balenoptera - viviparous (incorrect).
3. Analyze Delphinus - viviparous (incorrect).
4. Analyze Pteropus - viviparous (incorrect).
5. Analyze Ornithorhynchus - oviparous (correct).