What caused the four children to feel angry and confused?

The situation in which the four children feel angry and confused is tied to the impact of one of Mr. Curtain's message broadcasts. This broadcast not only conveyed messages that were perplexing but also held underlying manipulative intentions that affected the children's emotions. Mr. Curtain's broadcasts are designed to influence and control, and when the children hear them, they often experience a mix of anger and confusion due to the contradictory messages and the unsettling nature of his plans.

In contrast, the other options involve scenarios that might cause frustration or disappointment, such as receiving a bad grade or facing punishment. However, these contribute less directly to the core theme of manipulation and mind control present in the narrative. The unique emotional response of anger and confusion is most strongly evoked by the deliberate and confusing nature of Mr. Curtain’s communications, thus making the broadcasts the primary catalyst for their feelings in this context.