Which of the Following Is an Example of Spatial Summation

Which of the following is an example of spatial summation?

A) Two stimuli from two sources produce graded potentials on the same neuron at the same time such that the two potentials sum.
B) Two action potentials occur at the same time and sum.
C) Two rapid stimuli from the same source produce graded potentials on the neurons that sum.
D) An action potential occurs at the same time as a graded potential, and they sum.
E) A neuron sends out information through collaterals to several target cells.