Final answer:
When adding vectors, the magnitude of the resultant vector depends on the magnitudes and directions of the original vectors. If the vectors cancel each other out, the magnitude of the resultant vector will be zero.
Step-by-step explanation:
The magnitude of a vector is a measure of its length or size. When adding vectors, the magnitude of the resultant vector depends on the magnitudes and directions of the original vectors. The magnitude of the resultant vector is found using the Pythagorean theorem.
Let's consider a vector of magnitude 3 and a vector of magnitude 4. If the vectors are added in such a way that they cancel each other out, the magnitude of the resultant vector will be zero. This means that option A is correct.