Two Ideas, One Sentence
Card 1: The sign is tall. Card 2: The lower picture is beside Casey's stool. Card 3: the folded sheet
Join: The sign is tall, and the lower picture is beside Casey's stool. Another choice: The sign is tall, but the lower picture is beside Casey's stool.
Cards 1 and 2 each say something complete in this invented scene. Card 3 names something but is not the complete clause in this contrast. And adds the second idea; but offers a contrast. The author chooses a relation that fits the intended meaning. “Fold the sheet and press the crease” coordinates commands; it is not our selected demonstration of two explicitly supplied independent clauses.
Full picture description
Three separate strips carry the exact card wording and punctuation. Both complete joined sentences appear below. Numbers/text distinguish cards without colour.