Using the SAS data sets, DATA_1 and DATA_2,

DATA_1

ID DATE

123 1/31/2013

456 9/15/2014

789 6/5/2015

DATA_2

ID DATE

123 9/5/2014

123 6/22/2014

333 2/9/2015

456 11/15/2013

and the following data step, how many observations will be in the resulting SAS data set called THREE?

PROC SORT DATA = DATA_1; BY ID; RUN;

PROC SORT DATA = DATA_2; BY ID; RUN;

DATA three;

MERGE DATA_1 DATA_2 (in=aaa);

BY ID;

IF aaa;

RUN;

a) 3

b) 4

c) 5

d) 7