Why do I volunteer with Big Brothers Big Sisters of America? I have many reasons. Perhaps the biggest reason is that someone volunteered to help me. Years ago, I was on the other side of the table. I was lonely and felt kind of lost. More than once, I found myself on the wrong side of a jail cell(牢房). If someone hadn't stepped in, I probably wouldn't even be here right now.

    I've seen the work that Big Brothers Big Sisters has been doing all over the country and I'm pleased to be part of it. I've never done anything that made me prouder than my volunteering work. Big Brothers Big Sisters helped me get my head on straight. There are no words to describe the joy I get from helping somebody turn their life around.

    Don't tell anyone I said that, but volunteering is probably the fastest way to get over sadness or depression. Every time I start to feel bad, I talk to someone who needs my help and it makes me feel better and worse all at the same time. I feel better, because doing good things fills me with a sense of pride. I feel worse because I feel I have no right to complain about my situation especially when I hear what others are going through.

    I've come a long way from where I was. Volunteering is how I want to leave my mark on the world. I recommend volunteering work to everybody, especially for somebody who isn't sure where they're going in life. Helping someone find their path is often the best way to find yours.

我们规定：若 $\overrightarrow{m}$ =（a，b）， $\overrightarrow{n}$ =（c，d），则 $\overrightarrow{m}\cdot \overrightarrow{n}$ =ac+bd．如 $\overrightarrow{m}$ =（1，2）， $\overrightarrow{n}$ =（3，5），则 $\overrightarrow{m}\cdot \overrightarrow{n}$ =1×3+2×5=13．

1969年5月11日，《人民日报》向全世界报道了一则我国既无内债又无外债的消息。此后我国形成了不向国内外借债的财政政策，直到1979年12月，我国政府同意接受外国政府提供的第一批贷款，这一政策才被打破。这表明我国(  )