100. You can renew your contract within 30 days before the _ ____ DPUe. (A)val idity (B)extension (C)maturity (D)expiry 。

54. We appreciate your patience and please _____ that we will do everything i n our power to _____ that this type of error does not occur in the future. (A)assure....ensure (B)be assured....be ensured (C)assure.....be ensured (D)be a ssured....ensure 。