Concept:QBASIC uses line numbers to identify and organise each instruction in a program.Explanation:In QBASIC, the numbers 10,20,30,40,50,60, and 70 are written at the start of each program line.These numbers are known as line numbers.Line numbers show the order of execution of the statements.They also help the programmer jump to a particular instruction or edit a specific part of the program.Therefore, these numbers do not represent bullets or codes; they are simply line numbers.Answer:D. line number