III. The present perfect tense. 

1. Our teachers have explained the English grammar. 

1. The students have discussed the pollution problems since last week. 

1. Have the thieves stole the most valuable painting in the national museum? 

1. Have you finished the above sentences? 

1. They have given Tom a present. 

1. The weather has turned all the leaves yellow. 

1. A famous writer has written that book. 

1. I have just bought a new pen. 

1. They have awarded the best student a scholarship. 

1. They have already reported the result of the exam. 

1. They have sold thousands of CD machines since 1983 

1. He has broken his ankle in a football match.