The occasion or circumstance that leads the speaker to the thoughts in Sonnet VII would be
C. a birthday
Explanation:
Milton is remarking on the successes and failures of his life, staring at however previous he has become as a result of the recently turned twenty 3. This caused him to replicate on his life and deem his purpose and God's influence on his life path.
"How shortly hath Time the suttle theef of youth,
Stolen on his wing my three and twentieth year!"
These gap lines show that he feels the time has been 'stolen' from him on the arrival of his twenty-third year.
