ANS:B - bus contention

Bus contention occurs when two outputs drive the same signal at the same time, This reduces the reliability of the chip because it has multiple drivers fighting each other to drive a common output. If bus contention occurs regularly, even for short times, the possibility of damage to the drivers increases.

Bus contention can lead to erroneous operation, excess power consumption, and, in unusual cases, permanent damage to the hardware"such as burning out a MOSFET.

One place where this can occur, and that is often ignored, is during the turnaround of a bus. In a synchronous bus, when one device is driving the bus during one clock cycle and a different device is driving during the next clock cycle, there is a short time when both devices may be driving the bus.