Phytoplankton play a crucial role in the ocean’s uptake of carbon from the atmosphere. When alive, these tiny marine organisms absorb atmospheric carbon via photosynthesis.______after they die, the phytoplankton sink to the seafloor, where the carbon in their cells gets stored in sediment, preventing it from cycling back into the atmosphere.
Which choice completes the text with the most logical transition?
Explanation
Context: The passage describes how phytoplankton move carbon out of the atmosphere: while alive, they absorb it through photosynthesis. The blank introduces what happens after they die, sinking to the seafloor where the carbon is locked into sediment.
Answer: D) Then,
Why? Absorption during life and burial after death are consecutive stages of one process, so the blank marks the step that comes next in the sequence.
Traps:
- A) "Specifically," promises detail about photosynthesis in living plankton, but the sentence moves on to a later stage.
- B) "By contrast," sets the two stages against each other, yet both work to keep carbon out of the atmosphere.
- C) "Nevertheless," concedes something opposed to what came before, and sinking with stored carbon continues the process rather than countering it.