单项选择题 （）that dieting is fruitless for people who think that they are too fat，the alternatives are fairly limited.

单项选择题 Which of the following involves using the inherent strength of social networks to encourage visitors and fans to share their Likes and comments with friends？（）

填空题 Many of the at-risk behaviors of HIV and AIDS are actually related to cultural beliefs and （），while shaping by an array of complex social，economic，and political factors.