71.  I wannd to know which is the right answer and why.

72.  do you know when the tower was first built?

73.  But ice cream was known long before America was discovered.

74.  There is a story that be ordered his cook to keep the recipe for ice cream a royal secret.Today ice cream is known by the world.

75.  I knew few friends.

76.  I began to know the other friends.

77.  This week I know my result of this exam.

78.  I don't know some songs name .

79.  Though I don't know some words .

80.  But I knew I shouldn't waste time.