In which of the following, placenta development can not be seen?

Options

A. Human
B. Columba
C. Horse
D. Cattle

Answer

To solve the question "In which of the following, placenta development can not be seen?", we will analyze each option provided:

1. **Human**: Humans belong to the class Mammalia, and they develop a placenta during pregnancy. The placenta is essential for providing nutrients and oxygen to the developing embryo and for removing waste products. Therefore, humans do have a placenta.

2. **Columba**: Columba refers to the genus that includes pigeons and doves, which belong to the class Aves (birds). Birds do not develop a placenta; instead, they lay eggs, and the embryo develops within the egg. Thus, the development of a placenta is not seen in Columba.

3. **Horse**: Horses are also mammals and belong to the class Mammalia. Like humans, they develop a placenta during gestation, which is crucial for the nourishment of the developing foal. Therefore, horses do have a placenta.

4. **Cattle**: Cattle, like horses and humans, are mammals. They also develop a placenta during pregnancy to support the growth of the calf. Thus, cattle have a placenta as well.

After analyzing all the options, we conclude that the only organism listed that does not develop a placenta is **Columba**.

**Final Answer**: Columba (Option 2)