C. N(440,000)

Explanation:
To determine the net cash flow from investing activities, we look at the cash used for purchasing long-term assets and any cash received from selling these assets. The formula is:

$$\text{Net Cash Flow from Investing Activities}=\text{Proceeds from Sale of Motor Vehicle}-\text{Purchase of Property, Plant and Equipment}$$

Substituting the provided figures:

• Proceeds from the sale of motor vehicle: N10,000
• Purchase of property, plant, and equipment: N450,000

Calculating:

$$\text{Net Cash Flow from Investing Activities}=10-450=N(440,000)$$

This result indicates a net cash outflow of N440,000 from investing activities, reflecting that the cash spent on acquiring assets exceeded the cash received from selling assets.