Read the text.
Snowflakes are formed by water droplets freezing onto bits of dust in the atmosphere, but they come in many different shapes. The most well-known is the six-pointed, star-like snowflake, paper versions of which can be found in the windows of many classrooms. But some snowflakes are simple six-sided disks, and others are tiny six-sided columns. Two main factors determine the shape of an individual snowflake crystal: the temperature and level of moisture in the air. Colder temperatures, below -22°C (-7.6°F), produce simple disks and columns. The familiar star-shaped crystals form in warmer temperatures. And moister air gives rise to more complex shapes with more branches and details.
Which organizational structure does this text primarily use?