keeping
动词＋ing规则：
1、直接加ing:go – going; do – doing;
2、以不发音的e结尾,把e去掉加ing :
write – writing; ride – riding; skate-skating;
3、末尾三个字母以“辅＋元＋辅”构成的重读闭音节,双写末尾字母加ing :
swim – swimming; skip—skipping; sit – sitting;
put – putting; shop – shopping; run – running;
4.ie结尾的,把ie改为y再加ing：
tie－tying(系); die－dying(死); lie－lying(撒谎)