The sentence that best explains Kennedy's tone before the shift is A. He is offering help to friendly and democratic nations in our part of the world. His tone is promising.
Before the shift in tone, Kennedy used phrases such as "offer a pledge", "alliance for progress", "assist free men" and "cast off the chains of poverty". The firs three phrases are related to offering help, while the last one implies hope that the other countries' future will be bright and free of poverty.