Which one of the following fitness trends involves performing a specific exercise at a high intensity for 20 seconds, followed by 10 seconds of rest?

the answer would be Tabata Protocol and here is explanation of what it is

The study used 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). The exercise was performed on a mechanically braked cycle ergometer.