现阶段，重大建设工程主要有（）。

A.国家、省级重要的国防高端和科研建设工程

B.国家级重要的科研建设工程

C.省级重要的国防高端建设工程

D.国家和直辖市级重要的科研建设工程

Almost everyone likes dogs, and almost everyone likes to read stories about dogs.
I have a friend. He has a big police dog named Jack. Police dogs are very clever. Every Sunday afternoon my friend takes the dog for a long walk in the park. Jack likes these long walks very much.
One Sunday afternoon, a young man came to visit my friend. He stayed a long time. He talked and talked. Soon it was time for my friend to take Jack out for a walk. But the visitor still stayed. Jack became very worried. He walked around the room several times and then sat down in front of the visitor and looked at him. But the visitor paid no attention. He went on talking. At last Jack got angry. He went out of the room and came back a few minutes later. He sat down again in front of the visitor, but this time he took the visitor’s cap in his mouth.

The young man came to

A. pay a visit

B. see the dog

C. buy the dog