Which phrase best describes the mood established in these sentences from Silent Spring?

There was a strange stillness. The birds, for example—where had they gone? Many
people spoke of them, puzzled and disturbed. The feeding stations in the backyards
were deserted. The few birds seen anywhere were moribund; they trembled
violently and could not fly. It was a spring without voices.

Question 5 options:

mysterious and frightening

hectic and confusing

sad and regretful

bitter and angry