Vijay is a member of his school Eco Club. As part of Earth Day celebrations, he decides to contribute an article to the school magazine advocating the use of solar power as a step to mitigate the energy crisis.
Read a sentence from the draft of Vijay's article and help him complete it by selecting the most appropriate option.
Solar power is the ______to a clean energy future. That's why we need to ______heavily in solar plants for a better future.

Options

A. option, depend
B. reason, spend
C. key, invest
D. reason, install