I look forward _______ you.

 উল্লেখিত প্রশ্নের সঠিক উত্তর হচ্ছে - to hearing from.
- Complete Sentence: I look forward to hearing from you.

• Use of Look forward: 
- Look forward এরপর to + verb + ing বসে।

Example: 
- I look forward to hearing from you soon.
- I am looking forward to seeing you.
- My friend is looking forward to going to London.

• এছাড়াও mind, cannot help, could not help, with a view to, look forward to ইত্যাদি শব্দের পর কোনো verb বসলে সেই verb এর সাথে ing যুক্ত করতে হয়।

Source: CLIFFS TOEFL.