practice是以e结尾的动词，通常去e加ing，所以practice的ing形式是practicing
一般情况下，直接在动词后加－ing work ---- working sleep ----- sleeping study ----- studying
动词以不发音的－e结尾，要去－e加－ing take ----- taking make ----- making dance ----- dancing
重读闭音节的动词，要双写词尾字母，再加－ing cut ----- cutting put ----- putting begin ------ beginning 以－ie结尾的动词，把变成y再加－ing lie ----- lying tie ----- tying die ----- dying