question: time:speed
choices.label: A B C D
choices.text: space:quality volume:density pressure:efficiency price:value
explanation: when the distance is certain, the shorter the "time", the faster the "speed". there is no obvious logical relationship between "space" and "quality". when the mass is constant, the smaller the "volume", the greater the "density". there is no obvious logical relationship between "pressure" and "efficiency". the expression of "value" is "price". the lower the price is, the higher the "value" is not necessarily.