In the study of physics, what distinguishes a scalar from a vector?

a) A scalar is a dimensionless number, while vectors are numbers that have dimensions.
b) A scalar must always be positive, but vectors can be positive, negative, or zero.
c) A scalar is specified with a single number, but a vector is specified using both a magnitude and a direction.
d) Scalars have both a magnitude and a direction, but vectors have only a magnitude.
e) Nothing