Choose the correct answer.

35. Do you know who ____________ _ the fact that sound travels in waves?

36. I'm thinking of getting a fax ____________ _.

37. The ____________ _ of the outbreak of the disease is still unknown.

38. Ten million text messages are sent on ____________ _ every minute.

39. Once they've finished the extension to the ____________ _‚there'll be room for them to take on a lot more workers.

40. Shannen doesn't dye her hair; it's ____________ _ blonde.

41. I’ve ____________ _ it in at the mains but it still doesn’t seem to work.