阅读下面材料，有的答案要填入适当的内容，有的答案要用括号内单词的正确形式，但每个答案不多于3个单词。
Today，the ____（popular） of basketball has risen around the world，with many young people dreaming ____becming famous player．In China，you ____（see）people playing basketball now and then in parks，schools and even ____（factory）．Basketball has not onlu become a pilular sport to play，but it has ____become a popular sport to watch．Although America's NBA games are ____（famous） in the world，the CBA games are becoming more popular in China．____number of foreign players，including Chinese players，in the NBA has increased．There ____also more and more foreign players in the CBA．Many young people look up to these basketball heroes and want to become like ____（they ）These stars encourage young people____（work ） hard to achieve their dreams．
的自变量x的取值范围是__________________.