Much of the research on nutrient deficiencies is based on growing plants hydro-ponically,

Much of the research on nutrient deficiencies is based on growing plants hydro-ponically, that is, in soilless liquid nutrient solutions. This technique allows researchers to create solutions that selectively omit certain nutrients and then observe the resulting effects on the plants. Hydroponics has applications beyond basic research, since it facilitates the growing of greenhouse vegetables during winter. Aeroponics, a technique in which plants are suspended and the roots misted with a nutrient solution, is another method for growing plants without soil.

The word "facilitates" in the passage is closest in meaning to

A．slows down

B．affects

C．makes easier

D．focuses on

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