*Question E6C10:
In Figure E6-3, which is the schematic symbol for a NOR gate?*  

*Correct Answer is  D: 4*  

### AI Response: (may contain errors)  

In digital electronics, a NOR gate is a fundamental logic gate that produces a true output (1) only when all its inputs are false (0). 

### Explanation of the Correct Answer:
- **Correct Answer: 4**  
  The schematic symbol for a NOR gate typically consists of an OR gate symbol with a small circle (representing NOT) at the output. This indicates that the output is the inverse of the OR operation. 

### Explanation of Incorrect Choices:
- **Choice A: 1**  
  This symbol likely represents a simple OR gate, which outputs true when at least one input is true, not the inverted output of a NOR gate.

- **Choice B: 2**  
  This symbol may represent an AND gate or another type of logic gate, which does not reflect the NOR operation.

- **Choice C: 3**  
  This symbol could represent a NAND gate, which outputs false only when all inputs are true, again not matching the NOR function.

### Summary:
- A NOR gate outputs true only when all inputs are false.
- The correct symbol includes the OR gate shape with an inversion circle at the output.
- Remember that NOR is the combination of OR and NOT, which is crucial for identifying its schematic representation.

This understanding will help you recognize logic gate symbols in the exam and apply them correctly in circuit analysis.