The square root of 0.81 is

A. 9
B. .09
C. .91
D. .9

D. .9

To find the square root of 0.81, you can use a calculator or perform a series of calculations. Here's the step-by-step method:

1. Start with the number 0.81.
2. Take the square root of 0.81:

√0.81 = 0.9

Therefore, the square root of 0.81 is 0.9.

So the correct answer is D. 0.9