Mrs White had a problem. Her young son, Timmy, hated to go to bed at night. Mrs White read to him and gave him warm milk, but Timmy refused to fall asleep. No matter what she did, Timmy wanted to stay up. One day Mrs White had an idea.

    Ever since Uncle Charlie had taken him sailing, Timmy wanted to be a sailor. He loved fishing with his father. He loved to watch the waves wash against his hair. “some day,” Timmy said, “I'm going to have my own boat. And I'm going to be the captain.”

    So Mrs White had a boat built—one that could be hung from the ceiling in her son's bedroom. She felt that if he could sleep in the boat, he would want to go to bed at night.

    The boat builder made the boat and hung it in Timmy's bedroom. Timmy loved it.

    Finally Timmy was happy to go to bed.

下列地理现象中，与太阳活动密切相关的是(    )

设A为4×3阶矩阵，且r（A）=2，而B=$\begin{array}{ccc}1& 0& 2\\ 0& 2& 0\\ -1& 0& 3\end{array}$，则r（AB）=____ ．

将看到的中文转化成英文