使用urllib库定制http请求参数中的user-agent的方法是（ ）。
A headers = {'User-Agent':'Mozilla/5.0'}request = urllib.request.Request(url
Bheaders=headers)[|] headers = {'User-Agent':'Mozilla/5.0'}request = urllib.request.urlopen(url
Cheaders=headers)[|] headers = ['User-Agent'
D'Mozilla/5.0']request = urllib.request.Request(url
Eheaders=headers)[|] headers = ['User-Agent'
F'Mozilla/5.0']request = urllib.request.urlopen(url
Gheaders=headers)