Answer: Option 'B' is correct.
Explanation:
Since we have given that
A. The product of 3/4 and a number is 16.
The expression would be

B. 1/5 of a number
The expression would be

C. half of a number is 15
The expression would be

D. The difference of 20 and a number is 14
The expression would be

So, we can see that
is represented by a single expression.
Hence, option 'B' is correct.