正解　案内士になる The error is due to the lack of knowledge or misunderstanding of 「joshi」助詞（に、を、は）which is characteristic of Japanese language. If English you can simply connect verb(become　なる) and its obeject（guide　案内士）.　But in Japanese one must insert a joshi に in between. Another example. I play tennis. →　○　私は、テニスをします。　×　私、テニスします。