Tim Cook called his mother every week even while he_______ around the world.
A:was traveling
B:is traveling
C:traveled
D:travels
50-3×8=____ 70-81÷9=____ 25+5×7=____
南极洲有世界“寒极” 之称,其酷寒的主要原因是( )①跨经度最广 ②地处高纬度 ③绝大部分被冰雪覆盖 ④受海洋影响大