【单选题】We all agree that computers are essential ______ the problems of increasing population.
【单选题】1岁婴儿,未接种过麻疹疫苗,3天前接触过麻疹患儿,应采取的措施是
【简答题】Which one is not essential to be a good reviewer?
【单选题】The opening ceremony is a great occasion; it is essential ______ for that.[2003]