Which of the following alkaloids are good plant insecticides ?

Options

A. Nicotine
B. Pyrethrum
C. Cinerin
D. All of these

Answer

To solve the question "Which of the following alkaloids are good plant insecticides?" we will analyze each option provided: nicotine, pyrethrum, sinarin, or all of these.

### Step-by-Step Solution:

1. **Understanding Alkaloids**:
- Alkaloids are naturally occurring compounds found in plants that often have significant effects on living organisms. They can have various properties, including sedative effects.

2. **Analyzing Nicotine**:
- Nicotine is an alkaloid found in the leaves of tobacco plants. It is known for its insecticidal properties. When insects come into contact with nicotine, it acts as a potent insecticide.

3. **Analyzing Pyrethrum**:
- Pyrethrum is another alkaloid, which is derived from the flowers of certain plants, particularly chrysanthemums. It is widely used as a natural insecticide due to its effectiveness in killing a variety of insects.

4. **Analyzing Sinarin**:
- Sinarin is an alkaloid found in the roots and flowers of certain plants. It also has insecticidal properties and can help in controlling insect populations.

5. **Conclusion**:
- Since all three alkaloids—nicotine, pyrethrum, and sinarin—are known to have insecticidal properties, the correct answer to the question is "all of these."

### Final Answer:
- The correct option is **all of these**.