1. Can you really be best friends with someone of the opposite sex without ulterior motives?2. It is normal to be attracted to people of the opposite sex.
 the opposite sex the opposite gender異性(一人) = someone of the opposite sex異性(多人) = people of the opposite sex
老師 (讓小朋友出校車後): 別嬉戲，別跟陌生人說話。 (請填空)
Teacher (after letting kids out of the school bus on a field trip): No hrseplay. Don't talk to strangers.