What is the error on the subject-verb agreement?

modern calculators, which can compute sums almost instantaneously, derives from abacuses, hand operated devices with beads that slide along rods.

Which of the following quotations reveal an omniscient point-of-view? a. "then the king got his spear in both his hands and ran toward sir mordred, crying, 'traitor, now has thy death-day come! '" b. "and the king thought that under him, far from him, was hideous deep black water; therein were all manner of serpents and worms and wild beasts, foul and horrible." c. "but when the hosts on both sides saw that sword drawn, they blew trumpets and horns and shouted grimly, and the two hosts rushed toward each other." d."then they agreed that king arthur and sir mordred should meet between their two hosts, and that each of them should bring fourteen persons with him."

What details of the first two paragraphs convey a sense of the ordinary,behind the scenes routines of film critics?

Which sentence contains the central claim in "compulsory voting: an idea whose time has come" by tor hunter?