课时作业(三十) 选修6 unit 5 the power of nature ⅰ.单词拼写 1．when the train began to move quickly，helen excitedly________(挥手) at her friends on the platform. 2．most researchers believe that，in theory，mobile phones are________(绝对的) safe. 3．my time is________(珍贵的)；i can only give you a few minutes.
