Final answer:
c We have held the subject up in every light of which it is capable; but it has been all in vain... The quotation from Henry's speech that shows how parallelism emphasizes two ideas of equal importance is option c: 'We have held the subject up in every light of which it is capable; but it has been all in vain...'.
Step-by-step explanation:
The quotation from Henry's speech that shows how parallelism emphasizes two ideas of equal importance is option c: 'We have held the subject up in every light of which it is capable; but it has been all in vain...'.
Parallelism is a rhetorical device where similar grammatical structures are used to create balance and emphasis. In this quotation, the parallel structure of 'We have held...It has been...' repeats the structure to emphasize the equal importance of both actions. By using parallelism, the speaker highlights that despite their efforts, their previous actions were futile.
Therefore, option c is the correct answer as it shows how parallelism emphasizes two ideas of equal importance in Henry's speech.