researcher planned to conduct an independent-samples t-test to test for a difference between the number of math problems completed correctly by Group 1, who listened to nature sounds in the background during testing, and by Group 2, who listened to heavy metal music in the background during testing. Select the appropriate null hypothesis for a two-tailed hypothesis test. a. There is a difference in the average number of math problems completed correctly by participants who listened to nature sounds and participants who listened to heavy metal. b. On average, participants who listened to heavy metal solved more math problems correctly than those who listened to nature sounds. c. On average, participants who listened to nature sounds solved more math problems correctly than those who listened to heavy metal. d. There is no difference in the average number of math problems completed correctly by participants who listened to nature sounds and participants who listened to heavy metal