Final answer:
The correct answer is 'impetus' for the motivating factor and 'invincible' as it describes the hockey team's perception of being unbeatable.
Step-by-step explanation:
The sentence requires a word that explains the reason behind the hockey team's decision not to play. The right choice would be the impetus, which means a motivating factor or incentive.' Coupled with supposedly impervious, which suggests that the team is believed to be very strong or impossible to defeat, the correct sentence should read: 'What was the impetus for the supposedly invincible hockey team's decision not to play in the game?' Thus, the most suitable answer is option B. Impetus; invincible.