Construction of half/ full adder using XOR and NAND gates and verification of its operation

Half-adders have a major limitation in that they cannot __________
The difference between half adder and full adder is __________
If A, B and C are the inputs of a full adder then the sum is given by __________
If A, B and C are the inputs of a full adder then the carry is given by __________
How many AND, OR and Ex-OR gates are required for the configuration of full adder?