Answer: new
Step-by-step explanation:
A positive connotations are simply defined as the associations or the words which are affirmative and has a good feeling attached to it. A negative connotation brings about an uncertain or bad feeling.
Therefore, the word from this excerpt from William Carlos Williams's "Spring and All" that has the most positive connotation will be "new". Other words such as uncertain, lifeless and cold brings a negative connotation.