What problem does the enable input of a d flip-flop solve?
a. race conditions when flip-flops go too fast.
b. clock skew when gates are inserted in the path of clock signals.
c. incomplete reset when clock pulses are too short.
d. incomplete reset when clock pulses are too fast.
e. not knowing what state a flip-flop is in.

Athin walled concentric tube exchanger is used to cool engine oil from 160°c to 60°c with water that is available at 25°c acting as a coolant. the oil and water flow rates are each at 2 kg/s, and the diameter of the inner tube is 0.5 m and the corresponding value of the overall heat transfer coefficient is 250 w/m2. oc. how long must the heat exchanger be to accomplish the desired cooling? cpwater=4.187 kj/kg-candcpengine el=2.035 kj/kg·°c, oil . 120]