Question

phytoplankton play a crucial role in the oceans 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? a) specifically, b) by contrast, c) nevertheless, d) then,

Explanation:

The first - part of the text describes what phytoplankton do when alive (absorb carbon via photosynthesis), and the second - part describes what happens after they die (sink and store carbon). There is a contrast between the two stages of the phytoplankton's life cycle. "By contrast" is used to show a difference or opposition between two things, which is appropriate here. "Specifically" is used for giving more details about something already mentioned; "Nevertheless" is for indicating a contrast despite something; "Then" is for showing a sequence of events in a more general time - order sense.

Answer:

B. By contrast,