In the sentence "I'm sorry to hear you lost your bike," the correct word is "to."
Here's why:
1. "To" is used as a preposition to show the relationship between the subject and the verb in the sentence.
2. In this context, "to" indicates the action of hearing someone's loss.
3. The word "two" refers to the number 2, and "too" means excessively or also, which do not fit the intended meaning in this sentence.
Therefore, the appropriate word in the sentence is "to."
