Final answer:
A pulley system can have a mechanical advantage of 1 if it is a single pulley that changes the direction of the force without multiplying it. However, levers, inclined planes, and screws can also have an MA of 1 in specific configurations.
Step-by-step explanation:
A machine that has a mechanical advantage (MA) of 1 implies that the input force is equal to the output force; in other words, the force is not multiplied. Of the options provided, a pulley with an MA of 1 would essentially just change the direction of the input force without multiplying it. This can occur in a single pulley system where the pulley is only used to redirect the force. Similarly, a lever, inclined plane, or screw could, in specific scenarios, have a mechanical advantage of 1, but this depends heavily on their configuration. For instance, a lever with equal arm lengths and a load positioned equidistant from the fulcrum as the input force would also have an MA of 1.