Answer:
b. cart total + 1
Explanation:
A. cart total=1 do increment the total with every 1 click here, it only 're-assigns cart total with value 1 for every click, hence it's always 1.
B. In every click, 1 is always added to the previous value of cart total, like addItemButton(cart total+1) or so.
C. This would have worked too if "cart total" and "cartTotal" where of same type.
D. cart total is just being initially defined here.
E. Likewise here, var shows that cart total has just only been declared.