The correct option is A Approximately 120 cm
Length of the red dress = 100 cm
The blue dress is a bit longer than the red dress.
∴ Length of red dress > 100 cm
From the options, we can see that 170 cm, 190 cm, and 200 cm are far longer than 100 cm.
So, the length of the blue dress will be approximately 120 cm.
∴ Approximately 120 cm is the correct answer.