You have the right one selected.
The answer is 2:1
To find this take each side of ABC and its corresponding side on DEF, then simplify. You can treat ratios just like fractions, so simplify them in the same way.
20:10 becomes 2:1
12:6 becomes 2:1
16:8 becomes 2:1
A set of ordered pairs is called a relation. The set of all first components of the ordered pairs of a relation is the domain of the relation, and the set of all second components of the ordered pairs is the range of the relation. :)
The decimal equivalent of 3/10 is .3