根据句子意思,用所给单词的适当形式填空. 71 Their parents are both teachers And_(I) are doctors. 72.You can make a_(decide) among the suggestions. 73.THe law of gravity_(discover)by Isaac Newton about 350 scars ago. 74.He lives on the__(nineteen ) floor of the building. 75.We had better eat more_(harm ) vegetables. 76____(luck)all of them were hurt in the accident. 77.1 am going to the USA to have a_(far) study. 78 The Great Wall as well as the palace museum__(attract)lots of tourists from abroad every year. 79.We should do everything we can_(protect)the environment. 80.By 5:30yesterday afternoon he_(ftnish)writing the laboratory report.