AccordingtoCharlesKeeling,theamountofcarbondioxide

問題詳情：

According to Charles Keeling, the amount of carbon dioxide ________ sharply and steadily over the forty years between 1957 and 1997.

  A. increased                B. had increased     

  C. had been increased    D. was increasing

【回答】

A

知識點：動詞時態與語態

題型：選擇題