Which of the following conditions are sufficient and essential for a quantity to be a vector?

A vector is a quantity that has both magnitude (or size) and direction. In addition, vectors must satisfy certain algebraic properties, such as the ability to be added and subtracted, multiplied by a scalar, and divided by another vector using vector laws. Therefore, option C includes all the necessary and sufficient conditions for a quantity to be considered a vector. Options A and B do not include all the necessary conditions, while option D only mentions the combination of vectors by ordinary rules of algebra, which is not sufficient to define a vector.