According to the text, it can be inferred that

the two mass balance assemblies are made of two weights fastened together and fixed to the arm with two bolts.

According to the text, judge the following items.

There may be birds weighing more than 170 pounds.

According to the text, judge the following items.

Skydivers are a real hazard to airplanes.

According to the text, judge the following items.

A skydiver with an open parachute has such strength that he can slow an aircraft down.

According to the text, judge the following items.

Dangers related to mixing falling skydivers and flying aircraft can not be avoided.

According to the text, judge the following items.

The area planned for jumping may be threatening.

Based on the text, it can be deduced that

invariably the controllers are too busy to deliver their reports back to pilots.

Based on the text, it can be deduced that

jumpers try to search for traffic before exiting, and furthermore, the PIC of the jump aircraft regularly gets in touch with ATC to inform about the beginning of jump operations.

Based on the text, it can be deduced that

radio calls made through CTAF seldom include the airport where jump operations are occurring.

Based on the text, it can be deduced that

after the last parachutist leaves out the aircraft, the jump pilot reports to ATC that jumping is over.