he greatest possible length which can be used to measure exactly the lengths: 20 m 6 cm, 11m 90 cm and 14 m 45 cm is:Options :A.17B.18C.19D.121

To solve this problem, we need to convert all measurements to the same unit. Here, we will convert all measurements to centimeters:

• 20 m 6 cm = 2006 cm
• 11 m 90 cm = 1190 cm
• 14 m 45 cm = 1445 cm

The greatest possible length which can be used to measure exactly these lengths is the greatest common divisor (GCD) of these three numbers.

Let's calculate the GCD:

• GCD of 2006 and 1190 is 2
• GCD of 2 and 1445 is 1

So, the greatest possible length which can be used to measure exactly these lengths is 1 cm.

However, this option is not available in the given options. Therefore, there might be a mistake in the problem or the options provided.