The right answer is C. sex cells.
Like all cells, a somatic cell can mutate.
* A somatic mutation, if it is "viable" (if it does not kill the cell, organ or organism that carries it), and if it is not controlled by the body (apoptosis, confinement of the mutated cell) can give rise to new identical cell lines, thus carrying the same mutation.
* In so-called evolved animals (which can not clone naturally), this mutation affects only the organ or the organism concerned, but will not be transmitted to the offspring of the individual.