_________ the light bulb was commercially viable in 1879, it had not actually been perfected for mass use until carbon filaments were introduced.
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writingWhich choice completes the text so that it conforms to the conventions of Standard English?
A
Before
B
Since
C
Because
D
Although
Correct Answer: D
Choice D is the best answer. "Although" sets up the contrast between the 1879 viability and the later perfection.
Choice A is incorrect because "Before" creates a timeline confusion. Choice B is incorrect because "Since" implies cause. Choice C is incorrect because "Because" implies cause.