阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。
When I was 12, all I wanted was a signet (图章) ring. They were the "in" thing and it seemed every girl except me had one. On my 13th birthday, my Mum gave me a signet ring with my initials(姓名首字母) carved into it. I was in heaven.
What made it even more special was that it was about the only thing that wasn't being "re placed". We'd been burnt out in fires that swept through our area earlier that year and had lost everything—so most of the " new" stuff (东西) we got was really just to replace what we'd lost. But not my ring. My ring was new.
Then, only one month later, I lost it. I took it off before bed and it was missing in the morning. I was sad and searched everywhere for it. But it seemed to have disappeared. Eventually, I gave up and stopped looking for it. And two years later, we sold the house and moved away.
Years passed, and a couple of moves later, I was visiting my parents' when Mum told me that she had something for me. It wasn't my birthday, nor was it Easter or Christmas or any other gift-giving occasion. Mum noticed my questioning look. "You'll recognize this one," she said, smiling.
Then she handed me a small ring box. I took it from her and opened it to find my beautiful signet ring inside. The family who had bought our house 13 years earlier had recently decided to do some redecorations, which included replacing the carpets. When they pulled the carpet up in my old bedroom, they found the ring. As it had my initials carved into it, they realized who owned the ring. They'd had it professionally cleaned up by a jeweler before sending it to my mother. And it still fits me.
的渐近线与圆
相切，则
等于（ ）