Final answer:
Without the context of a geometric figure, we can't answer definitively. In a line segment scenario with points in order, if AE equals AB, then EC could potentially be 2 units. Further information about the figure is needed for a precise answer.
Step-by-step explanation:
The student has provided the lengths of three segments, AD, AB, and AC, presumably in a geometric figure, but hasn't specified the type of figure or the relative positions of the points. Without this information, we cannot directly calculate the measure of segment EC. However, we can provide a general explanation: if the points A, B, C, D, and E lie on the same line in the mentioned order, and all the points are distinct, AD is the entire length of the line segment from A to D, thus we would have AE + ED = AD. If AD is 10 units and AE is the same length as AB, then AE would be 8 units (assuming AE=AB), because AB is given as 8 units. Consequently, ED would be 2 units (since 10 - 8 = 2), and if E and C are the same point, then EC would indeed be 2 units. If the points do not lie on a single straight line or there are additional constraints, then further information would be necessary to solve for EC. None of the provided options (a, b, c, d) matches the result exactly. Please double-check the given values or the answer choices. If there's a mistake in the values, the correct answer can be determined based on the correct information.