There are a few words that could work here, but a common one is "respectable". If something or someone is respectable they are worthy of attention. There are other words as well.
Answer:
“Graduation is at seven o’clock, so don’t be late,” said Brian sternly.
Explanation:
the second sentence is wordy and out of order, making it harder to understand. the first sentence is straightforward and to the point
Answer:
C "Hence, more schools should follow the trend of starting later in the morning if they want to see improved test scores, greater attendance numbers, and, most importantly, healthier, happier teens."
Explanation:
I doubted it at first because it sounds too repetitive with sentence 13, but it makes more sense than the other options and relates to the argument and establishes a unified end as it summaries that more schools should have a later start time to help students succeed academically and improve their general wellbeing.