I would say the answer is probably A. Foreboding means <span>fearful or a feeling that something bad will happen, which makes the most sense in the context of the sentence.</span>
"Things only have meaning in context"
You can see this from the examples that Dickenson lists.
"Land by oceans past" - You would not be able to tell the land if there were no oceans
"Peace by its battles told" - How would we have a definition for peace without battles?
You can join the sentence in this way:
<em>Disappointed by not being able to picnic by the river, they went home sadly.</em>
The author can put the main character at a dangerous place. To cause tention.
Hope this helps....