题目

Last July, my parents and I went to visit my aunt and uncle in Seattle, a city on the northwest American coast. Dad did some research and had no difficulty in finding us cheap tickets online. On the day of our flight, we had to wake up very early. When we checked our bags in, we found that one bag weighed too much, so we had to pay a fine. After that, Dad insisted that we go and have some breakfast at the airport restaurant. We had a lot of fun watching many different people there. Then we realized it was getting late, so we rushed to the gate. It took one hour for everyone to get on t19 % 的MgCl 2 溶液中，Cl － 与H 2 O个数比为                         （    ） A．4∶90         B．4∶45         C．2∶45         D．19∶81