Parallel resistors, why? (Basic electronics)
Remove the ground from the schematic, and it should be obvious that R1+R3 is in parallel is R4.

Remember that ground is just the one point in a circuit we declare the 0 V reference to implicitly measure other voltages relative to.  In this case, no current can flow in or out of the ground connection since there is no other ground connection anywhere in this circuit.  Since no current flows thru the connection, you can remove it for the purpose of analyzing the circuit.