43. [A] prevent [B] hard [C] develop [D] open
44. [A] that [B] which [C] what [D] as
45. [A] they're [B] it's [C] there're [D] you're
46. [A] of [B] in [C] to [D] on
47. [A] smaller [B] bigger [C] newer [D] softer
48. [A] send [B] produce [C] store [D] destroy
49. [A] an [B] one [C] a [D] the
50. [A] its [B] our [C] their [D] your