首先,你舉的例中to take the exam是動詞不定式做賓語；其次我們可以說she decided on taking the exam.
不同的動詞,用不同的動詞不定式或現(xiàn)在分詞做賓語,需要專門記憶；
個別動詞既可接動詞不定式有可接現(xiàn)在分詞（我們更多時叫作動名詞）：like to do/doing sth.不定式表示偶爾或具體的行為,現(xiàn)在分詞表示經(jīng)常,抽象的行為.
i like reading. i like to to read this book .
動詞不定式和現(xiàn)在分詞做賓語補(bǔ)足語,區(qū)別如下：
see sb. do sth/see sb. doing sth
i saw him play football yesterday.
i saw him playing football at five.
動詞不定式表示動作完成及過程；動詞現(xiàn)在分詞表示動作正在進(jìn)行.