When you see an image of a solid the particles of the solid are usually packed but in fact there may be some between them.

When you see an image of a solid the particles of the solid are usually packed tight but in fact there may be some space between them.

1. tight/tightly

2. movement/space

why is arctic sea ice important? arctic sea ice keeps the polar regions cool and moderate global climate. sea ice has a bright surface; 80 percent of the sunlight that strikes it is reflected back into space. as sea ice melts in the summer, it exposes the dark ocean surface.

i think it's c. i'm not sure but i think so.