I forgot to include the following sentences. Thank you.

1) The last theme concern the fundamental questions whether time is preordained or the result of human activity.
2) The three witches stand for evil and are linked to the theme of equivocation.
3) They stayed/were/remained in power for 20 years.
4) It's the shortest of/among Shakespeare's tragedies.
3) Taxes were kept down (also low)
4) He wasn't born of a woman naturally since he was torn from his mother's womb by means of Casearian section.

1. theme (singular) concerns BUT the themes concern (plural)

Don't forget that Writeacher explained to you the use of the "historical present" when discussing literature. The literature IS, no matter when it was written.

Sra