This is the definitions given by Chinese Zero to Hero (paid). Video:
Everyone will see some pictures that come in pairs.
And their pdf translation:
Researchers have designed an interesting experiment. The volunteers’ task was simple, each of them would see pictures appearing in groups of two, one of each group came from the hands of a famous abstract artist, another would be a graffiti from a amateur, a baby, a chimpanzee or an elephant. Volunteers must decide which picture they liked better in each group.
So putting together 两两 = "in pairs", 一组 = "a group", and 出现 = "to appear", we get the above "appearing in groups of two". So they show the participants two images, and they choose the best one, then they show another two. (It reminds me of experiments like What Is The Best Thing? by Tom Scott.)
Be aware that the HSK texts are sometimes derived from original texts. In this case, it comes from:
周静嫣, 抽象艺术美不美, 科学画报, 2012.
The part in bold translates to something like "everyone will see a few groups of pictures appearing in pairs".