Choose the answer that best completes the sentence. zebra mussels can live six or seven years, now it seemed that most were dying after only one or two years.

C

Explanation:

A. Since

B. Because

C. Although

D. For example

Zebra mussels have been known to have a lifespan of six or seven years in the past but recent discoveries have shown that their average lifespan now ranges between one to two years. Hence, the correct word to fill in the gap would be 'Although'.

The correct option is C

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem

not: both offer magnification to the atomic level.