Final answer:
Without additional information on the angles and positions of the cables, it is not possible to calculate the required tension in cable AC or the resultant downward force. Hence, there is not enough information.
Step-by-step explanation:
The question requires an understanding of vectors and forces, specifically the concept of tension in physics. To determine the necessary tension T in cable AC such that the net effect of the two cable tensions is a downward force at point A, it is essential to know more details about the geometry of the situation—such as angles at which the cables are attached to the transmission tower, and the positions where the cables are anchored. Without this information, the question does not provide enough data to calculate the required tension in cable AC or the resultant downward force. Therefore, the answer is a. Not enough information.