The writer wants to add a sentence before sentence 8 (reproduced below) to introduce the main idea of the third paragraph. The data these devices provide are not as accurate as the data that come from a sleep lab.
36.)Which of the following sentences best accomplishes this goal?

A. It is difficult to say how accurate fitness trackers are when used at home, however, because most research on their effectiveness has been done in laboratory settings.

B. Aside from fitness trackers, there are many other tools for monitoring sleep, including smartphone apps and even devices that attach to bedsheets

B In addition, fitness trackers are becoming less expensive and more accurate as time goes on and technology improves.

C. One recent study compared the accuracy of seven different sleep tracking devices.

D. Granted, fitness trackers are not perfect tools.