An EX-OR gate can only have two inputs. The output of an EX-OR gate is true when its inputs are different (one true, one false).
Resistor A resistor restricts the flow of charge. Uses include limiting the current passing through an LED, and slowly charging a capacitor in a timing circuit. Some publications use the old resistor symbol
LDR A transducer which converts brightness (light) to resistance (an electrical property). LDR = Light Dependent Resistor