--When _____ the abacus _____? -- In the sixth century by the Chinese people.
A.is, invented | B.did, invent |
C.was, invented | D.does, invent |
--When _____ the abacus _____? -- In the sixth century by the Chinese people.
A.is, invented | B.did, invent |
C.was, invented | D.does, invent |