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.