The correct options are
A in parallel, the combination acts as a fuse of rating 20A
C in series, the combination acts as a fuse of rating 10A.
A fuse is a piece of wire resistance which acts in a way such that if the voltage in a circuit exceeds the rating of the fuse then the fuse wire melts and the circuit becomes an open circuit, thereby breaking the circuit and preventing the components from getting damaged due to short circuit. Now, if two fuses are in series, the melting of a single fuse can break the circuit and so in series the rating will be 10A. However, in parallel, even if one fuse is melted, the other fuse still works and so the net rating will be 20A.