A Fat Goblin quest…reinforcements question

By builderChris, in Descent: Journeys in the Dark

in the set up for A Fat Goblin quest (encounter 1) it tells me that my Monsters are Goblin Archers and 1 open group. it tells me to place the goblin archers on the exit and the open group on the grass lands.

than, under the reinforcements section of the set up it says: " At the start of each overlord turn, he may place 1 goblin archer on the Exit and 1 monster from the open group on the Entrance, respecting group limits. These monsters may be activated during the turn they are placed".

so here is my question.

can the 1 monster from the open group that i place on the entrance be a monster from any open group that qulifies for this encounter or am i limited to only placing 1 monster from the 1 open group that i selcted from the Monster section of the set up?

for example: during set up, the monsters that are avaibale for me to select from are the Merriod, the Barghest, the Cave Spider and theFlesh Moulder. if the 1 open group i selected at the start of the encounter was the Merriod (the 1 open group i placed on the Grasslands) at the start of my turn can i place 1 Barghest ("1 monster from the open group") on the entrance? and than at the start of my next trun place 1 Cave spider and than at the start of my next trun place 1 Flech Moulder? OR am i stuck with only placing 1 Merriod since that was the 1 open group i selcted at the beginning of the quest?

in other words does the "the" in "…and 1 monster from the open group on the entrance…" refer to the 1 open group selcted during setup or does the "the" refer to any of the qulifiying monsters in the open group?

thanks.

The open group is the one you picked at the start of the encounter - all other monsters are not ascessible.