请教这题答案问什么选D?能否详细解释一下IN？谢谢！

42.Assume that SAS data sets Sasdata.Products and Sasdata.Sales both contain the
Prod_ID variable. Which of the following SAS DATA steps returns only exceptions or
non matches?
a. libname sasdata 'SAS-data-library';
data all;
merge sasdata.products
sasdata.sales;
by prod_id;
if ins=1 or inp=1;
run;
b. libname sasdata 'SAS-data-library';
data all;
merge sasdata.products(in=inp)
sasdata.sales(in=ins);
by prod_id;
if ins=1 and inp=1;
run;
c. libname sasdata 'SAS-data-library';
data all;
merge sasdata.products(in=inp)
sasdata.sales(in=ins);
by prod_id;
if ins=0 and inp=0;
run;
d. libname sasdata 'SAS-data-library';
data all;
merge sasdata.products(in=inp)
sasdata.sales(in=ins);
by prod_id;
if ins=0 or inp=0;
run;