B

Test question analysis: When we help others selflessly, others will also help us. This shows that the contradictory parties will transform into each other under certain conditions, ③ "Blessings and misfortunes" and ④ "lost harvest", as two contradictory parties, are interdependent and can transform into each other under certain conditions, which is consistent with the philosophy contained in the question; ① embodies the need to look at problems from a comprehensive perspective; ② embodies The principle of dialectical relationship between quantitative change and qualitative change. Choose B for this question.