The correct answer is: machine.
‘Please’ and ‘Thank you’ are the little courtesies by which we keep the machine of life oiled and running smoothly.
A path is a way to get from one place to another. It can be a physical path, like a trail in the woods, or a metaphorical path, like a journey through life. A path is not something that needs to be oiled or kept running smoothly.
A machine is a device that is used to do work. Machines can be simple, like a lever, or complex, like a computer. Machines need to be oiled and kept running smoothly in order to work properly.
A garden is a place where plants are grown. Gardens can be small, like a window box, or large, like a farm. Gardens need to be watered and cared for in order to thrive.
A river is a large stream of water that flows through the land. Rivers can be calm or turbulent, and they can be used for transportation, irrigation, and recreation. Rivers do not need to be oiled or kept running smoothly.
In conclusion, the correct answer is: machine.