Kelly想成为一名工程师可以用 "Kelly wants to become an engineer." 表示。
"want" 是动词，表示 "想要"。
"to become" 是介词短语，表示 "成为"。
"an engineer" 是名词短语，表示 "一名工程师"。
例句：
"Kelly has always wanted to become an engineer." (凯莉一直想成为一名工程师。)
"Becoming an engineer is Kelly's long-term goal." (成为一名工程师是凯莉的长期目标。)
"Kelly is studying hard to achieve her dream of becoming an engineer." (凯莉正在努力学习实现成为工程师的梦想。)