Which pair of expressions below contains like terms?
a. 7x and 8xy
b. 12x and 12y
c. 5xy and 7xyz
d. 3yz and 9yz

D. 3yz and 9yz.

Step-by-step 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.