5 By the time he became a well- known writer, he had already travelled to several European countrys.

Ответ

By the time he became a well-known writer, he had already travelled to several European countrys.

В данном предложении необходимо заменить существительное "countrys" на "countries", так как оно стоит во множественном числе.

By the time he became a well-known writer, he had already travelled to several European countries.

Ответ: countries