Answer:

D. 2/3

Step-by-step explanation:

Steps to simplifying fractions

Find the GCD (or HCF) of numerator and denominator

GCD of 18 and 27 is 9

Divide both the numerator and denominator by the GCD

18 ÷ 9

27 ÷ 9

Reduced fraction:  

2

3

Therefore, 18/27 simplified to lowest terms is 2/3.