The primary purpose behind roosevelt’s words in this excerpt is to
a) impress the public with emotional diction.
b) inspire the public to join the military.
c) convince the public of america’s strength.
d) encourage viewers to remain active.

The Roosevelt's words were:
I cannot prophesy. I cannot tell you when or where the United Nations are going to strike next in Europe. But we are going to strike—and strike hard.

Through all those words he was trying to convince the public of America’s strength. Also, President Roosevelt's primary purposes in his State of the Union address were to convince the public to support an idea, to encourage the public to unite and to motivate the public to take action.