Choose the correct alternatives (more than one may be correct) and write the corresponding letters only:
All digital circuits can be realized using only
Half-Adder, and MUX both need help of constant 1, and can realize all logic circuits, hence B,C are the correct options.
Half Adder is partially functionally complete not fully functionally complete.
They didn't Ask you only functional complete
They just asking "All digital circuits can be realized using only"
so, here comes both partially FC and FC
So, Answer should be B and C