Urgent help PHP Devil Training Camp [Make a personal blog from scratch] An error occurred after importing the project

Question

错误提示：Parse error: syntax error, unexpected '[' in C:\myphp_www\PHPTutorial\WWW\myblog\public\tpl\page_tpl.php on line 3 

if (count($_GET)==0 || (array_keys($_GET))[0]=='page'){
   $prefix = '?';
}