
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
The $7\times21$ rectangle $ABCD$ is cut into two pieces in such a way that they can be rearranged without overlap to form a triangle. What is the altitude of the resulting triangle from its base?
A) 12 units  
B) 13 units  
C) 14 units  
D) 15 units  
E) 16 units

Present the answer in LaTex format: \boxed{Your answer}
user