题目

We did a survey about unpaid work among 300,000 married couples in our city. One third of them have no children, another third have one or two and the last third have three or more. The unpaid work includes childcare and housework. The diagram（图表） on the right shows the result of the survey. 正确的涂 A，错误的涂 B 。 1． According to the diagram, “more children” means “less unpaid work” for husbands. 2． We can infer unpaid work done by wives with over 3 children will rise to over 50 hours a week. 3． The survey shows childcare usually falls on wives. 4． The△ABC中，∠A=，BC=，向量=（-，cosB），=（1，tanB），且⊥，则边AC的长为    ．