根据短文理解, 从A、B、C、D四个选项中选择最佳答案填空。
An old friend from the US whom I was looking forward to staying with telephoned from the airport to tell me that he had arrived. I was still at the 1 at that time, but I had got everything ready for his arrival. After letting him know where my house was, I told him that I had left the 2under the doormat(门垫), 3 I was likely to be home rather late. I told him to go into the 4 and help himself to food and drink. Two hours later my friend 5 me from the house. At the moment, he said, he was listening to some of my records after having just had a truly wonderful 6 . He had found a cooker and 7 two eggs and he helped himself to some cold chicken from the ice box. He said he was drinking a glass of orange juice and he hoped I would 8him. When I asked him if he had reached the house without difficulty, he answered, "I was not able to find the key, 9 luckily, the living-room windows Just by the apple tree were left open and you know what I could do." I listened to all this in 10 . In front of my living-room there was no apple tree at all.
这个三角形的周长是( )