Which of the following best illustrates feedback in development ?

Options

A. As tissue ( X ) develops it secretes something that slows down the growth of tissue (Y)
B. Tissue (X) secretes RNA which changes the development of tissue (Y)
C. As tissue ( X) develops it secretes enzymes that inhibit the development of tissue (Y)
D. As tissue ( X) develops it secretes something that induces tissue (Y) to develop

Answer

To solve the question regarding which option best illustrates feedback in development, we can break it down step by step:

### Step-by-Step Solution:

1. **Understanding Feedback in Development**:
- Feedback mechanisms in development refer to how one tissue or organ can influence the growth and development of another through signaling molecules or hormones.

2. **Analyzing the Options**:
- **Option A**: "Tissue X develops and secretes something that slows down the growth of tissue Y."
- This suggests a negative feedback mechanism, but it does not illustrate a direct interaction that promotes development.

- **Option B**: "Tissue X secretes RNA which changes the development of tissue Y."
- This indicates a change in development but does not specify whether it promotes or inhibits growth.

- **Option C**: "As tissue X develops, it secretes an enzyme that inhibits the development of tissue Y."
- This is another example of negative feedback, where tissue X is inhibiting tissue Y, which does not illustrate a positive developmental interaction.

- **Option D**: "As tissue X develops, it secretes something that induces tissue Y to develop."
- This option indicates that tissue X is actively promoting the development of tissue Y, which is a clear example of positive feedback in development.

3. **Identifying the Correct Answer**:
- Based on the analysis, **Option D** is the best illustration of feedback in development, as it shows a direct influence of one tissue on the development of another in a positive manner.

### Final Answer:
The correct answer is **Option D**: "As tissue X develops, it secretes something that induces tissue Y to develop."

---