Dilution and concentration question

Using a 10.0 mL pipette, an aqueous solution of hydrogen chloride is taken, which is then brought to 100 mL in a calibrated flask by adding water. 50.0 mL of the dilute solution react with 10.0 mL of 1.00 mol/L aqueous potassium hydroxide solution.
What is the molar concentration of the starting aqueous hydrogen chloride solution?

Choice 1
0.20 mol/L

Choice 2
1.0 mol/L

Choice 3
2.0 mol/L

Choice 4
4.0 mol/L

Hi everyone,
The answer is choice 3), could i have a step by step solution?
Thank you!

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