Answer:
The last option is the only correct one if you like to multiply
The second last option is good if you like to divide.
Step-by-step explanation:
Each fraction in the last two options has a value of 1
example
dividing by 1
15 cm /(100 cm/ 1 m) = 0.15 m 0.15 m / (1000 m/ 1km) = 0.00015 km
and
multiplying by 1
15 cm(1 m / 100cm) = 0.15 m 0.15m(1 km/1000m) = 0.00015 km
only one of the two fractions in each of the top two options has a value of 1.