Which of the following is unisexual?A     TaeniaB     NereisC     HirudinariaD     Pheretima

To determine which of the given organisms is unisexual, we first need to understand the reproductive characteristics of each:

1. Taenia: This is a genus of flatworms, commonly known as tapeworms. They are generally hermaphroditic, possessing both male and female reproductive organs.

2. Nereis: This is a genus of polychaete annelids (marine worms) that typically exhibit sexual dimorphism, meaning they have distinct male and female individuals, making them unisexual.

3. Hirudinaria: Also known as medicinal leeches, these organisms are usually hermaphroditic, like Taenia.

4. Pheretima: This refers to a genus of earthworms, which are also commonly hermaphroditic.

Final Answer

The unisexual organism among the options is B. Nereis.