@achievement = ('level A1', 'level A2', 'level A3', 'level A4', 
'level A5', 'level B1' , 'level B2', 'level B3', 'level B4', 
'level B5', 'level C1' , 'level C2', 'level C3', 'level C4', 'level C5', );

while (@achievement) {
     my $level = shift @achievement;
     push (@result, $level);
     print "Result: @result\n";
     }


##</code><code>##

Result: Level A1
Result: Level A1 Level A2
Result: Level A1 Level A2 Level A3 
Result: Level A1 Level A2 Level A3 Level A4
Result: Level A1 Level A2 Level A3 Level A4 Level A5
Result: Level B1
Result: Level B1 Level B2
Result: Level B1 Level B2 Level B3 
Result: Level B1 Level B2 Level B3 Level B4
Result: Level B1 Level B2 Level B3 Level B4 Level B5