The convex lens is used in-

Options

A. Microscope
B. Telescope
C. Projector
D. all of the above.

Explanation

**Step-by-Step Solution:**

1. **Identify the Applications of Convex Lens:**
- A convex lens is a converging lens that is thicker in the center than at the edges. It is commonly used in various optical devices.

2. **Check Each Option:**
- **Option A: Microscope**
- In a compound microscope, both convex and concave lenses are used. The convex lens is used to create a magnified image of the object.
- **Option B: Telescope**
- A telescope typically uses both concave and convex lenses. The convex lens is used as the objective lens to gather light and form an image.
- **Option C: Projector**
- In a projector, a convex lens is used to focus and project the image onto a screen. This is a common application of convex lenses.
- **Option D: All of the Above**
- Since convex lenses are used in microscopes, telescopes, and projectors, this option includes all previous options.

3. **Conclusion:**
- Since convex lenses are used in all the mentioned devices (microscope, telescope, and projector), the correct answer is **Option D: All of the Above**.

**Final Answer:**
The convex lens is used in all of the above options (A, B, and C). Therefore, the correct option is D.

---