To determine the reliability of the sentences, we can analyze each one:
A. "The first pioneers to explore the opal fields found an unpleasant and unfriendly environment." - This sentence can be considered reliable if it is based on historical accounts of the experiences of the pioneers.
B. "None of the pioneers liked summer because it was dreadfully hot." - This statement is a broad generalization about all pioneers and lacks specific evidence. It is likely unreliable since it assumes the feelings of all individuals.
C. "To adapt to the challenging environment, pioneers built underground homes." - This sentence appears reliable as it reflects a known historical adaptation to harsh conditions.
Based on this analysis:
A is reliable, B is unreliable, C is reliable.
So the correct response is: A is reliable, B is unreliable, C is reliable.