what have you been up to?后面的那个up to 是怎么回事

what you have been doing what have u been doing的been是什么时态? What have you been up to lately? what have you been up to?中文翻译 What have you been up too lately? What have you been up to? what have you guys been up to? What have you been doing lately? what have you been up to lately? what have you been up to? what have you been up to today. what are you up what have you been up to where are you going?和where have you been 和what have you been? what have you been up to与 how have you been有什么区别? what have you been up to 还是 how have you been up to how have you been and what have you been up to. U have no Idea what I have been ThoughU have no Idea what i 还有这句··· 翻译：what have you been learning so far?