✔ 最佳答案
Sometimes a word can be different parts of speech in different sentences. For example,
This is a book. (book is a noun)
I have booked two tickets. (book is a verb)
The word "to" can be used as a preposition, an adverb or a particle.
We often see "to" being used as a particle to bring out an infinitive, e.g. I want to go home. This is the reason why you think that it should be "hear" instead of hearing.
In "looking forward to", the "to" is a preposition. A preposition is always followed by a noun, pronoun or gerund, e.g. I have already returned the book to the library.
Therefore, every time you see or use the word "to", you have to know whether it is a preposition, a particle or an adverb.
If you want to improve your English, you should start with the basic grammar rules.
