Consider the following quantities :
1. Real power
2. Reactive power
3. Power factor
4. Input current
5. Bus voltage magnitude
6. Bus voltage phase-angle
For the purpose of the load flow studies of a power system, each bus or
node is associated with which one of the combination of the above four
quantities?
1,3,4 and 5
1,2, 3 and 4
2, 3, 5 and 6
1,2, 5 and 6
1,2, 5 and 6
At any bus of the system,
these are four variables 
In a load flow two out of the four quantities are specified and the remaining two are required to obtained through the solution of the equation.
Hence, the correct option is (D).
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