72.___the beef being cooked on the stove,the mother pictured the whole family having meals together.(look)
看着炉子上炖着的牛肉,妈妈想象着一家人在一起吃饭的画面。
Looking at/When/While (she was) looking at
根据以上思路可知答案为:Looking at或者When/While (she was) looking at。
前面分词的逻辑主语应与后面主句的主语保持一致,且与主语构成逻辑上的主谓关系。也可以在前面加上表示伴随的时间连词when/while。
容易漏掉介词at。