The Triangular Snowflake
Snowflakes form from tiny water droplets, (1) following a specific process of chemical bonding as they freeze, which results in a six-sided figure. The rare “triangular” snowflake, similarly, (2)confounded scientists for years because it apparently defied the basic laws of chemistry. [A] The seemingly triangular shape of those snowflakes suggests that forming (3)through a different process of chemical bonding. [B] By re-creating snowflake formation, a discovery has revealed to scientists Kenneth Libbrecht and Hannah Arnold the cause of this apparent variation.(4)
Snowflakes begin to form when water in the atmosphere freezes it causes (5) the water molecules to bond into a hexagonal shape. During the flake’s descent from Earth’s upper atmosphere, other water vapor molecules bumps (6)into the hexagonal structure. Bypassing the liquid water phase, (7)those molecules condense directly onto the established hexagonal pattern. As a result, the flake grows outward into bigger and more complex hexagonal arrangements surrounding the original hexagonal shape at the center of the flake. [C]
In 2009, Libbrecht and Arnold’s experiments revealed that triangular snowflakes begin with the same process of chemical bonding and forms (8) a hexagonal shape. The triangular shape is an illusion resulting from one significant addition to the process (9)dust.
Triangular snowflakes begin to form when a tiny dust particle or other such impurity collides with the flake as it falls, thereby pushing one edge upward. [D] The downward edge of the snowflake encounters more wind resistance than the rest of the flake. The greater the pressure from the wind, (10)causes bonds to form quick (11)at this edge than in the rest of the snowflake.
The resulting snowflake has three long sides and three sides that are so short they are difficult to detect. Although these snowflakes appear to have a triangular shape— (12)they actually have a hexagonal pattern. Such snowflakes offer evidence that even when impurities interfere, the basic laws of chemistry still apply (13)
A. NO CHANGE
B. the manner in which formation
C. which had formed
D. that they form