长方形的长是4.2×103cm,宽为2.53×102cm,求长方形的面积.
1.05×106cm2
----Is that Jack speaking?
----Sorry, he isn’t in right now. He ________ the park with his mother.
A. have been to B. has gone to C. has been to
()在试运行前应对整机进行全面检查,所有零、部件是否安装准确、牢固、无误。