4 . Be cautious of Friday the 13^th！Many people think the day is unlucky.    1    （fortune）, there's only one Friday the 13^th this year. As the legend goes，you should try not     2    （break）any mirrors，walk under a ladder，or even spill any salt. Why？Researchers say    3     is tough to find out how the tradition came into being. Many believe it has     4    （religion）origins. In the Christian faith，there were 13 guests at table for the Last Supper，which was held the day before the Friday    5    Jesus died. Now，Friday the 13h has become a cultural wonder. Many Americans avoid the number 13 all together，    6    （include）hotel rooms and airplane seat assignments. It even costs couples less to get married on the day. There are many other    7    （explain）behind the luckless day. Simon Bronner，a professor of American studies at Pennsylvania State. University，    8    （believe）Friday the 13h is a way for people to pin their bad luck to a certain cause:. The fact should be    9    there's nothing special about the number itself. After all，the number 13     10    （consider）to be lucky in some countries，like Italy