A diode is required to work at a voltage of 600 V, and needs to supply a current of 0.35 A.  Which one would you use?  Explain your answer.             

The 1N4001 diode can provide a current of 1.0 A, so will be able carry the current of 0.35 A. (P)

However its working voltage is too low. (P)

The BY127 has a working voltage of 1250 V, and can supply 1.0 A.  Therefore it would be the diode to use. (P)