70+80____70+60 5800–800____6000–3000 130+70____200+20
700–90____700–80 1200–200____1000+200 500–50____400+50
100+50____200–60 100–60____100-70
如图一组图片呈现的是德国小伙儿威廉的生活片断。为他的快乐生活提供了如此便利的直接原因是( )