The main theme is the fragility of sanity, guilt versus innocence, and the unrelenting passage of time. The fragility of sanity: the narrator's attempt to prove his sanity, his erratic mannerisms while he explains his meticulous plans for killing the old man only prove his madness.
Subsequent is a time later or more recent than.
I'd say it's definitely D
Sergei's reaction is hostile. He is not interested in answering
Participles are words that are formed from verbs but act as adjectives. They are called <em>verbals</em>. What is more, phrases are a group of words without a subject and a verb that function as as single part of speech. Therefore, participles consist of the participle and its complements and modifiers.
Taking all this into account, it can be said that the participial phrase is "trimmed that morning" and that it modifies the noun "grass". This is a past participle which is further specified by the NP "that morning" which gives information about the time in which the grass was trimmed.
