求助data step， create a dataset with unique values ，input dataset 需求

同理注意45题 给出的答案是C是否也不对

To create a list of unique Customer_Id
values from the customer data set, which
of the following techniques can be used?
technique 1: proc SORT with NODUPKEY and OUT=
technique 2: data step with IF FIRST.Customer_Id=1
technique 3: proc SQL with the SELECT DISTINCT statement
A.
only technique 1
B.
techniques 1 and 2
C.
techniques 1 and 3
D.
techniques 1, 2, or 3


C :if first need sort