Если еще актуально:
program z;
const n=3;
var a,b:array[1..n] of real;
c:array[1..(2*n)] of real;
i,k:integer;
begin
for i:=1 to n do
readln(a[i]);
for i:=1 to n do
readln(b[i]);
k:=1;
for i:=1 to n do
begin
c[k]:=a[i];
writeln(c[k]);
k:=k+1;
c[k]:=b[i];
writeln(c[k]);
k:=k+1;
end;
end.