I took an English grammar test and one question was:
Chen's looking forward ... his new job next week.
There were four choices: to starting / to start / starting / in starting.
My answer was "to start", because I knew the structure of "looking forward to" and because of the presence of "to", I used the infinitive.
But the answer was "to starting". Why "V-ing" is used in this case? Is there a rule for “to + v-ing”?