Which of the following can be used to measure heart rate?

Researchers were interested in whether relaxation training decreases the number of headaches a person experiences. they randomly assigned 20 participants to a control group or a relaxation training group and noted the change in number of headaches each group reported from the week before training to the week after training. which statistical analysis should be performed to answer the researchers' question?

Which of these triangle pairs can be mapped to each other using two reflections?

If a || b and b | y, then ? a) x || y. b) x | a. c) a | y. d) a || y.