According to the study, the number of Americans who reported at least one severe sunburn rose from 30% to 39% ______.

A．their patients will soon get older
B．adults are diagnosed with skin cancer
C．there is an outbreak of deadly aches on the skins
D．many younger people suffer from skin cancer

A．spending too much time on vacations
B．going to the tanning gatherings too much
C．exposed too little to the sun
D．doing too many exercises