Fill in the blank (idiom: keeping life running smoothly) “'Please' and 'Thank you' are the little courtesies by which we keep the ______ of life oiled and running smoothly.” Choose the best word to complete the idiom.

Given data

• Idiomatic phrase describing smooth day-to-day functioning.

Concept/Approach
The fixed English idiom is “the wheels of life/industry/etc.,” often paired with “oiled.”

Option analysis
wheels — correct idiomatic choice (“keep the wheels … oiled”).gears — mechanical but not the usual collocation in this idiom.routes/paths — do not fit the “oiled and running” metaphor.

Final Answer
wheels