快回答thankyouEnglish

The format is: RUN + in + a race

She is running in the morning race at 10:00.
She is running in the 100-metre race at 10:00

Morning race is a compound noun. (boat race, marathon race)
Race should be singular. She can run only in one race at 10:00. (not races)

The format: AT a place (at the race)

In the second sentence, the emphasis is on the location, not the time.
I want to cheer for you and Jenny at the afternoon races.
I want to cheer for you and Jenny at the 100-metre races.
I want to take picture at the race.
I want to cheer for you and Jenny at the theatre.

Don’t be distracted and misled by the word "morning" or "afternoon". They are used to form a compound noun. Technically it has nothing to do with time. Only in the first sentence, "at 10:00" is a phrase that deals with time.

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If the word with the suffix “–tion” is a noun:

noun + s turns into a plural noun.

e.g. station + s = stations.

If the word with the suffix “–tion” is a verb:

Verb + s = singular verb used for third person.

Mention + s = mentions (singular verb)

She mentions her mother.

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“WHOM” is a pronoun.
It is used as object of a verb:

Whom did you see? (very formal English)
Who did you see? (normal English)

"Whom" can be used as object of preposition:

To whom it may concern: (as in a letter)
With whom did you go? (formal English.)