user
When I go up I am the present  When I go down I am the past   What am I
A: birthday
B: presentation
C: see saw
D: nowadays
E: present and future
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

C

<|end_of_solution|>