Which of these will create an empty Pandas dataframe named "empty$\_$df$"?$

$1.$

import pandas

empty$\_$df $=$ pd$.$DataFrame

$2.$

import pandas as pd

empty$\_$df $=[]$

$3.$

Import pandas as pd

empty$\_$df $=$ pd$.$DataFrame$()$

$4.$

import pandas

empty$\_$df $=$ pd$.$DataFrame$()$