Answer: D. 3yz and 9yz.
Explanation:
In an algebraic expression , the like terms are the terms that have the exact same variables with the same power or exponent.
A. 7x and 8xy , here y is not present in "7x" but present in '8xy' , so they arfe not like terms.
B. 12x and 12y , here variables are different in both terms , so they arfe not like terms.
C. 5xy and 7xyz , here z is not present in "5xy" but present in '7xyz' , so they arfe not like terms.
D. 3yz and 9yz , here the variables 'yz' are exactly same in both the terms, therefore , they are like terms.
Hence , the correct answer is D. 3yz and 9yz.