如题所述
ä»å¥æ¯è¿å»è¿è¡æ¶æwas/were doing,主å¥è°è¯ç¨è¿å»æ¶æ,ä¹å¯ä»¥æ¯è¿å»è¿è¡æ¶æãWhen I was singing, my mom called me.
I was reading while my mom was cooking.