In the development of the human body, the ectoderm is responsible for the formation of

Options

A. lens of the eye
B. nervous system
C. sweat glands
D. all of these

Answer

### Step-by-Step Solution:

1. **Identify the Germ Layers**: In human embryonic development, there are three primary germ layers: ectoderm, mesoderm, and endoderm. Each layer is responsible for forming different tissues and organs in the body.

2. **Define Ectoderm**: The ectoderm is the outermost germ layer that forms during the process of gastrulation. It plays a crucial role in the development of various structures in the body.

3. **List Structures Formed by Ectoderm**:
- **Epidermis**: The ectoderm gives rise to the epidermis, which is the outer layer of skin.
- **Cornea and Enamel of Teeth**: It also forms the cornea of the eye and the enamel of the teeth.
- **Lens of the Eye**: The lens, which is crucial for vision, is formed from ectoderm.
- **Nervous System**: The entire nervous system, including the brain and spinal cord, develops from the ectoderm.
- **Sweat Glands**: Ectoderm is responsible for the formation of sweat glands in the skin.

4. **Analyze the Options**: When presented with options regarding what the ectoderm forms, we can conclude that all the mentioned structures (lens of the eye, nervous system, and sweat glands) are indeed derived from the ectoderm.

5. **Conclusion**: Therefore, the correct answer to the question is that the ectoderm is responsible for the formation of the lens of the eye, the nervous system, and the sweat glands.

### Final Answer:
The ectoderm is responsible for the formation of the lens of the eye, the nervous system, and sweat glands.

---