Complex sentence: The 737's main landing gear under the wings at mid-cabin rotate into wells in the aircraft's belly; the legs being covered by partial doors, and "brush-like" seals aerodynamically smooth (or "fair") the wheels in the wells.
Split into simpler sentences: The 737's main landing gear under the wings at mid-cabin rotates into wells in the aircraft's belly. The legs are covered by partial doors, and "brush-like" seals aerodynamically smooth (or "fair") the wheels in the wells.