题目内容
完成句子
他正在做癌症之起因的研究工作。
He is carrying out a ________ into the ________ of cancer.
他正在美国访问。
He is ______ ______ _______ ______America.
他正在节食以减轻体重。
He is ________ to reduce some weight.
He is ________ ________ ________ to reduce some weight.