Saying no can be very difficult. People who are very shy often have little confidence.  They think that they have to meet everyone's need. It is very hard for them to say no. they sometimes feel shy if they say no, but doing things that they don't want to will make them unhappy.
A simple and direct “No” is the best way. If you want to explain, you can keep it simple. Just say, “No, I've already made plans for this time” or, “Sorry, I'm afraid I'm not free at that time.”
Other ways of saying no:
▲       I can't do this right now.
▲       No, but thank for asking.
▲       Please accept that I cannot come.
▲       I'd rather not.
To say no you should:
▲       Start the sentence with the word no.
▲       Shake your head when you say no to make sure they understand. Your voice should be clear and direct. Keep eye contact.
    If someone makes a request, it is necessary to ask for time to think it over. The decision should be up to you, but sometimes it is difficult to say no. You can try to reply in the following way:
   “Sorry. I would have taken care of your cat next weekend, but I will be going out. I know it will be hard to find someone to take care of the cat. I will try to help you next time.” Remember that: you have the right to say no!

根据下面的一段文字,给“拍客”下定义。不超过40字。

互联网时代出现了这样一群人:他们有社会责任感和爱心,眼界开阔,留意生活中的点点滴滴,从中择取社会“热点”,用手机、数码相机或数码摄像机等数码设备拍下图像或视频,用来表达对百姓生活和人文历史的理解与思考,然后以发送彩信或电子邮件的方式,上传到网络分享、传播。他们被称作“拍客”。成为“拍客”,不需要高超的摄影技术,妇孺皆可,老少皆宜。