The plane leaves x The planes leaves: Qual utilizar

Olá,

Estou com uma dúvida no uso do pronome "to leave" com a terceira pessoa no singular e no plural.

Eu estava resolvendo alguns exercícios do livro "Graded exercises in English" do Robert J. Dixson sobre plural de substantivos (página 9) quando me deparei com uma aparente incongruência.

O comando dos exercícios é: Change the subjects of the following sentences from singular to plural.

A questão 5 é a seguinte:
5. The plane leaves from this airport.

Minha resposta foi: The planes leave from this airport.

Contudo, ao conferir a resposta do livro, encontrei a seguinte frase: The planes leaves from this airport.

Não entendi o porquê de uso de leaves em vez de leave com um sujeito plural (planes).

De início achei que era erro de impressão ou algo do tipo, mas vi que a frase é recorrente na internet.

Alguém sabe dizer o porquê?

APRESENTAÇÃO PESSOAL EM INGLÊS
Nesta aula, a professora Camila Oliveira ensina como você deve se preparar para fazer uma apresentação pessoal profissional em inglês. O conteúdo dessa aula ajudará você a aproveitar melhor as oportunidades no ambiente corporativo. ACESSAR AULA
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NeyF 3 24 206
Está errado, o correto é "the planes leave".
PPAULO 6 49 1.3k
Hi there, Thiago.

Perhaps you have seen sentences like "Years come and go with ups and downs, happy and sad, good times and bad." (meaning - the years come and go). If not I have taken it from the web by way of example.

One more to the table:

The Bus Station a place where people come and go par excellence should play an interactive role with the contemporaneity providing comfort upon arrival and illusion in departure.
Notice that "people" here is plural, it would be nonsense to think such a crowded place with "people" in the plural form, we are talking about people in a general way here not a particular one, so many people.

Now, all you need to do is to follow the pattern anywhere else, which was what you tried to do.
Congrats on spotting the mistake. By the way, books might contain mistakes made in haste or sometimes the person responsible for the printing/editing may think of "helping". And here you are with an actual mistake! Even though, it´s not usual.
So, this is an important lesson you have just learned (and all of us), it´s that regardless the level of literacy of the author of a work, you have to read and use your critical thinking as well.
PPAULO 6 49 1.3k
A little correction:

Notice that "people" here is plural, it would be nonsense to think such a crowded place with "people" in the singular form.

Thanks heavens you understood the message anyway!