Which of the following is an example of the third form of cooperation as it is defined in Paragraph 4

A．Students form a study group so that all of them can improve their grades.

B．A new business attempts to take customers away from an established company.

C．Two rival political parties temporarily work together to defeat a third party.

D．Members of a farming community share work and the food that they grow.

井下集电器与架空线的接触压力一般为（）。

A、29～39N

B、39～49Ｎ

C、49～59N

D、59～69N