å 为æªæç¡®æ¶æï¼æ¬å¥å¯ä»¥æ两ç§ç¿»è¯æ¹æ³: â I am sitting under the tree with them. â¡I was sitting under the tree with them. 解æ: 第ä¸å¥æ¯ç°å¨è¿è¡æ¶ãåºæ¬æææ¯am/is/are+doingï¼è¡¨ç¤ºä¸»è¯æ£å¨åççå¨ä½æåå¨çç¶æã 第äºå¥æ¯è¿å»è¿è¡æ¶ï¼åºæ¬æææ¯was/were+doingï¼è¡¨ç¤ºä¸»è¯è¿å»æ个æ¶å»æ£å¨åççå¨ä½æåå¨çç¶æã äºè å·®å«å¨äºå¨ä½åççæ¶é´ã