The citric acid cycle is a cycle because the starting molecule, , is regenerated at the end.

Oxaloacetate

Oxaloacetate

Explanation:

At the end of this series of reactions, the four-carbon starting molecule, oxaloacetate, is regenerated, allowing the cycle to begin again. In the first step of the cycle, acetyl CoAstart text, C, o, A, end text combines with a four-carbon acceptor molecule, oxaloacetate, to form a six-carbon molecule called citrate.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current