Separate signed attack advantage from damage clipped at zero

A board game uses eight-sided dice. The attack die has five faces marked 0, two marked 1 and one marked 2. After the attack throw, the defender throws a defence die with two faces marked 0, four marked 1 and two marked 2. Damage is attack score minus defence score, except that a negative difference gives zero damage.

Let A,D denote the attack and defence scores.

(i) Write down their distributions. Hence find the expectation and variance of $A-D$.4 marks

X is the damage in one round.

(ii) Find its distribution, expectation and variance.5 marks

(iii) Explain why $E(X)>0$ although $E(A)<E(D)$.1 mark