第一题是 明显的时态错误.as引导的是时间状语从句,插入进了主句的谓语和宾语之间,常规顺序是Few people could have guessed (C.how pessimistic) she had been about her chances (D.of beating ) her opponent,as they (A .watch) Anna win the tennis match with (B.apparent) ease.
主句谓语和改宾语从句谓语已经用了过去式could have guessed和she had been about,所以要将从句的谓语watch改成watched
第二题并不是楼上所说的缺谓语.而是谓语动词应该用第三人称单数.这个句子的主语是The aquatic weed ,called "giant salvinia" 是The aquatic weed的定语,后面which是定语从句修饰giant salvinia",句子的谓语是threaten,后面many freshwater ecosystem是threaten的宾语.鱿鱼主语是The aquatic weed所以谓语动词threaten要改成threatens