user
What costs nothing but is very hard to find and can easily be lost?
A: test
B: racquets
C: true friendship
D: bill
E: a loyal partner
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

C

<|end_of_solution|>