
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
A pattern in a "stair-step" design consists of rows of squares, beginning and ending with a white square, with alternating black and white squares in between. In this modified design, starting from the second row, each succeeding row contains 1 more square than was added to form the previous row (i.e., 0 additional squares are added to the 1st row to form the 2nd, 1 additional square to the 2nd to form the 3rd, 2 additional squares to the 3rd to form the 4th, etc.). Determine the number of black squares in the 20th row.
A) 83
B) 84
C) 85
D) 86
E) 87

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