The correct option for the blank is - out of doors
In the sentence, En Plein air" is a French phrase that means in the open air.
Instead of creating artwork in a studio using references like photographs or other images, it refers to the practice of painting outdoors, directly from nature.
In the given sentence, Rosa is said to have painted nature ‘en Plein air’, which means she had painted outdoors.
Thus, the correct sentence is - Rosa was one of the first artists known to have painted nature ‘en Plein air’ or out of doorsAnswer:
Step-by-step explanation: