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Some may argue that bateries containing cadmiujm actually offer a partial solution to the problem by being rechargeable, and thus adding to the lifetime of a battery.
why is there using "adding" rather than "add" in the sentence?
"Some may argue that batteries containing cadmium actually offer a partial solution to the problem by being rechargeable, and (which is) thus, adding to the lifetime of a battery."
add or adding 
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