两条平行线间可以画无数条垂线．

To ________ somebody or something means to protect somebody or something from attack or danger.

   A couple of years ago, I went to a lady's house to buy some medicine. Upon entering the house, I1that there was a piano in the living room beside the wall.Being a piano music lover and player, I asked if the woman played. She said “Yes” and2that she had been taking lessons—at the age of 54!
   “I have been3for 8 years now.” I said, after hearing her words.“Then you must play a song for me before you leave,” she requested(请求).
   I thought she was kidding and I4smiled. When I had bought the medicine, she asked me to play some music. I thought for a moment and 5to play David Lanz’s Return to the Heart,6she had so much passion(热情)for and interest in music, and it’s one of my favourite songs.
   I played the song to the best of my ability(能力), putting as much emotion into it as possible. She7it. As I was about to step out of the door, I heard a weak voice calling, “Young man!”I8, and saw an old lady taking one little step at a time with the help of another woman. “I wanted to come out to thank you for the9song that you played. I have been very sick, and it's very hard for me to get out of bed, but I really wanted to thank you for the song. It made me feel good.” she said. With that, she turned around and walked slowly back to her room.
   I was deeply touched by her10and felt a deeper understanding for the song. It was11to its name, returning to one’s heart to12and joy. 

水的硬度常用一种规定的标准来衡量。通常把1 L的水中含10 mg CaO(或相当于10 mg CaO的物质)称为1。Ca^2＋、Mg^2＋的硬度之和称为总硬度。总硬度在8以上的水称为硬水。例如某水样分析含Ca^2＋44 mg/L，含Mg^2＋18 mg/L，则通过Ca^2＋～CaO和Mg^2＋～CaO的关系式，计算出1 L这种水相当于含103.6 mg CaO，即总硬度为10.4。

现在我区某地用水所含Ca^2＋、Mg^2＋、HCO₃^－物质的量浓度如下：

c(Ca^2＋)＝1×10^－3mol/L、c(Mg^2＋)＝5×10^－4mol/L、c(HCO₃^－)＝8×10^－4mol/L。

通过计算回答：