单项选择题
A.let user =’Barret’；console.log（’Hi ${user}!’）；//输出：Hi Barret!
B.var id =1；var url =’http：//localhost/api/messages/${id}’；
C.var user ={first_name：’howsun’，last_name：’zhang’}；var message =’Your name is ${user.first_name}${user.last_name}.’；
D.以上都不对