题目

After my husband died from a heart attack, my world changed all in a sudden. I just put all my effort into making a living, caring for the children and just keeping my head above water.I was lucky to find a wonderful housekeeper to care for the children during the week, but from Friday nights to Monday mornings, the children and I were alone, and in fact I was uncomfortable. Every unusual noise and any late-night phone call would fill me with fear. I felt unbelievably alone. One Friday evening I came home from work to find a big beautiful German shepherd （牧羊犬） on our doorstep. I beca在观察小麦根尖结构的实验中，我们可以通过放大镜观察到根尖上有很多的绒毛．这些绒毛集中生长的部位是根尖的（ ）A．成熟区B．分生区C．伸长区D．根冠