Final answer:
The word 'infallible' is best defined by the word 'perfect,' meaning incapable of errors. A hypothesis is closest in meaning to a suggestion, and a heuristic is a mental shortcut for problem-solving.
Step-by-step explanation:
The word infallible in the sentence "He believed his decision-making process to be infallible." means incapable of making mistakes or being wrong. Hence, the word that most closely defines infallible is 'perfect' (d). On the contrary, 'flawed' (a), 'error-prone' (b), and 'unreliable' (c) represent the opposite of being infallible.
As for the multiple-choice questions provided for reference:
- The word closest in meaning to hypothesis is 'suggestion' (d).
- A mental shortcut used as a general problem-solving framework is known as a 'heuristic' (b).