I like school days. I can learn many things from school. We have four classes in the morning and two in the afternoon. I like weekends, too. We don't go to school on Saturdays and Sundays. I often play ping-pong and play basketball on Saturday morning. I often play the violin (小提琴) on Saturday afternoon. I often do homework and play football on Sunday morning. I often go to the park on Sunday afternoon.

（2015.海南）据统计，1945年8月，国民政府的法币发行量累计为5569亿元，三年后增至604.6万亿元。引发严重通货膨胀的重要原因是国民政府（    ）

胚胎干细胞由于全能性高且在体外培养时具有无限增殖的特性，是胚胎工程生产和研究中常用的材料．但由于细胞在连续的分裂中过程，DNA大部分时间都在进行复制，可能出现许多复制错误，导致DNA出现损伤．下列叙述正确的是（　　）