A student carries out an investigation on a steel spring. First, he records the spring’s length, then he suspends different weights from it. For each weight, he measures the spring’s length. The table presents his results. A weight of $3.0\ \text{N}$ is hung from the spring. What is the extension of the spring?
- A$4\ \text{mm}$
- B$12\ \text{mm}$
- C$40\ \text{mm}$
- D$120\ \text{mm}$