Explanation:

- Option 1: Fervent

- "Fervent" means having or showing passionate intensity. It doesn't fit in any of the blanks.

- Option 2: Portent

- "Portent" means a sign or warning that something, usually momentous or calamitous, is likely to happen.

- It fits well in all the blanks:

- "One encouraging portent is that more people are using the railway network."

- "The savage civil war there could be a portent of what's to come in the rest of the region."

- "To have an owl calling about your house was usually read as an ominous portent for those inside."

- Option 3: Fervor

- "Fervor" means intense and passionate feeling. It's not suitable for any of the blanks.

- Option 4: Deterrent

- "Deterrent" means something that discourages or is intended to discourage someone from doing something. It doesn't match the context of the sentences.

- Option 5: Intent

- "Intent" refers to the purpose or aim. It also doesn't fit into the sentences contextually.