根据下面资料，回答题
Awareness Weeks(认知宣传周)have become a regular part of Britain´s cultural land-scape over the past few years． They started back in 1957, when one charity(慈善机构),Christian Aid, decided to´ make all its money-raising efforts on one time of year． It was thought that by doing this they would get more publicity for their cause．
They were right, and soon other charities and campaign (活动)groups followed them．
These days,most donations(捐款)to charity are not collected on the streets． So instead of just asking for money,charities prefer to spend their time" raising awareness"—spreading knowledge of the work they do or the cause they support． They also compete with busines-ses and trade groups who use Awareness Weeks as marketing campaigns for their products．
There are now 500 Awareness Weeks held every year in the UK． No week goes by without one group or another trying to make the British public aware of something, with most held in May or October．
The danger with all these Awareness Weeks is that people start to become cynical(不信任)． Take National Smile Week for example,it seems like a great idea．．" Let´s all make each other´s life a little bit happier with a friendly smile． "But really it´s just a group of dentists and cosmetics companies trying to sell us toothpaste． It´s enough to make you want to start National Forget About It Week．
"People feel that many awareness campaigns are just marketing exercises,"says Ms Ormiston,who edits the Awareness Campaign Register, a news letter which encourages people who run Awareness Weeks to become more aware of each other． "But 90 per cent of campaigns are run by traditional charities or not for groups to make money．"
"There´s still no official group for awareness campaigns," says Ms Ormiston． "People can do what they like,whatever the size of their budgets(经费)or their public relations ma-chines allows．"
This situation has led to calls for laws to stop real charities having their efforts over-shadowed by marketing campaigns． This could be done by making the two groups hold their weeks at different times or stopping businesses running imitation (模仿) charity campaigns．
But there is another way． Maybe it´s time for National Weak Awareness Week, espe-cially for people whose awareness of Awareness Weeks is weak．
 What´s the main purpose of Awareness Weeks run by charities in Britain?