Tissues are

Options

A. Groups of cells which are similar in origin and function
B. Groups of organs which are similar in origin and function
C. Cells which are similar in function but not in origin.
D. Groups of cells which are not similar in origin and function.

Answer

**Step-by-Step Solution:**

1. **Understanding Tissues**: Tissues are defined as a group of cells that work together to perform a specific function. They share similarities in their origin, structure, and function.

2. **Analyzing the Options**:
- **Option A**: "Group of cells which are similar in origin and function" - This aligns with the definition of tissues.
- **Option B**: "Group of organs which are similar in origin and function" - This describes organs, not tissues, so it is incorrect.
- **Option C**: "Cells which are similar in function but not in origin" - This contradicts the definition of tissues, which must have a similar origin.
- **Option D**: "Group of cells which are not similar in origin and function" - This is also incorrect as it does not reflect the characteristics of tissues.

3. **Conclusion**: Based on the analysis, the correct definition of tissues is represented by **Option A**: "Group of cells which are similar in origin and function."

**Final Answer**: Tissues are a group of cells which are similar in origin and function (Option A).

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