题目

After moving to the United States, immigrant groups trying to fit in tend to choose high calorie fatty foods in an attempt to appear more American, a new study finds. That's one reason why immigrants approach US levels of obesity within 15 years of moving to America.The researchers also did an experiment that measured whether or not the threat of appearing un-American influenced respondents’ food choices. After being questioned about their ability to speak English , 75 percent of Asian-Americans identified a typical American food as their favorite. Only 25 percent of Asian-Americans who had 若点A（a，1）与点B（﹣5，b）是关于原点O的对称点，则a+b＝_____．