_______ is well known, _______ Hong Kong returned to China on July 1st, 1997.
54. The football fans cheered their team _____ the entrance _____ the field.
53. Our music teacher often enjoyed _____ playing the violin in his spare time.
52. The struggle against sand storm will not end _____ victory unless we pay much attention to the balance of nature.
51. Don’t put your cell (手机) _____ the edge of the table, or it will fall off
50. The Englishman has a very good ear _____ music. You can ask him for some advice.