The correct answer is (B): a spring scale can be used in an investigation of the efficiency of different simple machines A spring scale is used to measure weight (force) of a load. When determining efficiency of a machine, we must know energy used to perform a certain work or activity and for us to do that we have to know the amount of effort or energy required or used in that situation, since, a spring balance can measure weight (force), then it can be very handy in the process of measuring the efficiency of a simple machine. The other choices (A),(C), and (D), in those situations, the spring balance cannot be of any use.