Answer:
When inspiration lags, and feeling sleeps.
Step-by-step explanation:
Amy Lowell's poem "Summer" is a description of the many seasons of the year. And to the poet, in particular, summer is "the very crown of nature's changing year", which she likes better than other seasons.
In the poem, the poet used the word "alone" towards the end of the whole poem. And in this word, we can make several readings to it. One such way to read it is "when inspiration lags, and feeling sleeps". This is because, summer is when everything seems to be in a trance, slow and 'drowsy' with no one interested to get around and play about. And for the speaker/ poet, it is when she's alone and gets no inspiration to write.
Thus, the correct answer is the fourth/ last option.