The noun "action" is singular; it is the singular form of "actions".

名词“ action ”是单数，他是“ actions ”的单数形式。

youdao

This noun appears in the singular form, never in the plural form.

这个单词只有单数形式，没有复数形式。

youdao

English people use the singular form of the noun in expressions of that sort.

英国人在这类词组中，常用名词的单数。

youdao

It would be great if the word (economic) cycle only existed in a singular form, and the only cycle we had in the economy was happy expansion.

FORBES: Chinese Quest For Shortcut To Greatness

And if it has not, the knowledge that both this group and one in Mexico are close to finding the genes which give the new form of maize its singular advantage should certainly do so.

ECONOMIST: Genetic engineering