The correct option is D 6:7
Given, the ratio is 18:21.
Here, antecedent = 18 and consequent = 21
We could write it using the word "to," as ''antecedent to consequent'' which is 18 to 21.
We can write a ratio as a fraction by writing the antecedent of the ratio as the numerator, and the consequent of the ratio as the denominator which is 1821.
Simplify and cancel out the common factors, we get
1821=3×63×7
=67
which can also be written as 6:7.
Hence, all the options are correct.