The pronoun is is because pronouns are such words like,as,IS, and others.
So the pronoun is is
Agricultural systems.
Natural Systems.
Artificial Systems.
Social Systems.
The correct option is this: THE WARM TEMPERATURE WILL COMPLICATE THE FAMILY'S HIKE.
From the passage given above, it can be seen that the author has carefully chosen the setting in order to pave way for the proper development of the play. The unexpected warm weather experienced by the family members when they emerge from their car will surely affect their enjoyment of the hiking session.
