Mashaal Masha
Human-made (synthetic) fibers used in clothes and many other consumer products are more durable than most natural plant ________ the manufacture of synthetic fibers requires toxic chemical solvents that can pollute air and water.

Which choice completes the text so that it conforms to the conventions of Standard English?
Difficulty: Easy
A: 

fibers,

B: 

fibers but

C: 

fibers

D: 

fibers, but

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