To assess the reliability of the sentences, we need to consider the context and the nature of the statements made:
A. "The first pioneers to explore the opal fields found an unpleasant and unfriendly environment."
- This statement is likely reliable as it reflects a common experience of early pioneers in harsh environments.
B. "None of the pioneers liked summer because it was dreadfully hot."
- This statement could be subjective. While it's plausible that many pioneers found summer hot and uncomfortable, saying "none" is an overgeneralization without specific evidence.
C. "To adapt to the challenging environment, pioneers built underground homes."
- This statement appears reliable as it aligns with historical practices of pioneers in harsh environments who built underground homes to cope with extreme weather conditions.
Based on this analysis:
- A is reliable.
- B is unreliable (due to the absolute term "none").
- C is reliable.
Thus, the correct answer is: A is reliable, B is unreliable, C is reliable.