Read this passage from the episode: 

They've learned what farmers can do to help keep cows happy and calm. Cows like soothing voices better than the sound of people shouting. Cows are happier when humans speak softly. Also, cows seem calmer when they are given names.

Which phrase from the passage helps you understand the meaning of the word soothing? 
given names
can do to help
speak softly
sound of people

speak softly