Read the summary of this section birth of an idea what is the best way to combine and shorten the sentences in this summary

Senator Nelson worked on environmental causes with little progress until 1969 when, inspired by Vietnam War protestors, he called for Earth Day- a National day of teach-ins about the environment.

Senator Nelson worked on environmental causes with little progress until 1969 when, inspired by Vietnam War protestors, he called for Earth Day- a National day of teach-ins about the environment.

Explanation:

my best guess would be: d allusion

makes the most sense

im not 100 percent sure but i think its a