IKMC 2021 - Grades 11-12 - Set 2 - Self-study Question 12

Question 12

Let $A=(0,1)\cup(2,3)$ and $B=(1,2)\cup(3,4)$, all intervals open. What is the set of all $a+b$ with $a\in A,b\in B$?

$(1,7)$
$(1,5)\cup(5,7)$
$(1,3)\cup(3,7)$
$(1,3)\cup(3,5)\cup(5,7)$
None of the previous choices