请阅读下面一段程序:import pandas as pd
import numpy as np
from datetime import datetime
date_list = ['2015/06/01','2016/02/01','2016.6.1','2018.6.1']
date_index=pd.to_datetime(date_list)
date_se = pd.Series(np.arange(4),index=date_index)
()
若需要获取2016-06-01对应的数据,则下列选项中可以填写到横线处的是()