If a reader did not know that ellery queen is normally associated with the mystery genre, which sentence would first indicate that "object lesson, part 1" is a mystery?
a) ellery hurried down west 92nd street toward the main entrance of henry hudson high school stealing guilty glances at his watch.
b) miss carpenter, who had come to him with an unusual request, had struck him as the sort of dedicated young person who would not take kindly to a hitch in her crusade.
c) beyond establishing that the crimes were the work of the same boys, who were probably students at henry hudson high school, the police had got nowhere.
d) miss carpenter, walking home from a movie late the previous monday night, had seen three boys dive out of a smashed bakery window and vanish into an alley.

d) Miss Carpenter, walking home from a movie late the previous Monday night, had seen three boys dive out of a smashed bakery window and vanish into an alley.

Explanation:

This is the excerpt that would indicate that this story is a mystery. In this excerpt, we learn of how a person was witness to a crime. We learn that Miss Carpenter saw some boys leaving a bakery and vanish into an alley. They had clearly broken into the business, as the window was smashed. This happened late at night, which increases the mysterious mood of the event.

Explanation:

It is between C and D, and likely either would do. Why would anyone (or 3 anyones) jump out of a broken window and head down an alley? Mighty suspicious if you ask me.

As for C, the police are involved, they have established some sort of identity of 3 boys who are guilty of something (crimes) and the school these three go to, the police know nothing. This is not a romance, but it might not be a mystery either.  It could be an identity problem.

I'll choose D because it has better detail.

I can't zoom sadly, But we can at least just chat on here. You seem pretty nice