Answer:

Explanation:
If two fractions are equal, they form a proportion.
Therefore, to determine if two ratios form a proportion, rewrite the fractions so that their denominators are the same, then compare.

As the two fractions are not equal, they do not form a proportion.

As the two fractions are equal, they form a proportion.

The denominators of these two fractions are already the same.
Therefore, as the two fractions are not equal, they do not form a proportion.

As the two fractions are not equal, they do not form a proportion.