In 'She wrote a letter', the verb 'wrote' is transitive and the word 'letter' is the direct object.

在She wrote a letter一句中，动词wrote是及物动词，letter一词是直接宾语。

《牛津词典》

Right. Well, here "will" is used as a transitive verb

这里的will却是用作了动词，加了ed

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This word is a transitive verb. We can use a noun or noun phrase as its direct object.

这是一个及物动词，我们可以用名词或名词性短语直接作其宾语。

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