Answer:
The success of the clubs in convincing the public that photography could be art was the agent of their: D) continued growth.
Step-by-step explanation:
The photography clubs that emerged in the late 19th and early 20th centuries were instrumental in elevating photography from a mere hobby or technical pursuit to a recognized art form. They held exhibitions, lectures, and competitions that showcased the artistic potential of photography and encouraged photographers to create works that demonstrated their artistic vision and skill.
As more people began to appreciate photography as an art form, the popularity of these clubs grew, and they continued to thrive as important centers of photographic art and education. Therefore, the success of the clubs in convincing the public that photography could be art was the agent of their continued growth.