Identify a good strategy for editing essays for spelling errors.
a. correct the essay while prewriting to catch errors early.
b. make a clean, error-free final copy of an essay.
c. look for the errors in the essay immediately after drafting.
d. let the draft sit for an hour or so before editing it.

I would say 'd'. It's  always better to give a fresh look to your paper. 
Well, I can definitely tell you that proofreading and editing are extremely important for the  the successful paper. I used to contact Supreme essay service. Those guys usually both proofread and edit my papers. So you can definitely give them a try. Good luck!

I would say it is D.

Use the following questions to check your response:

Do the verbs agree with their subjects?Are any words misused or misspelled (such as to, too, and two, and effect/affect)?Do the sentences use correct punctuation? (Check for commas, periods, semicolons, and colons.)Are there any incomplete sentences?Do sentences containing multiple ideas follow a parallel structure?