Answer:
Explanation for this statement has been given below.
Step-by-step explanation:

To convert temperature in Celsius scale, we have to add 273 with the given temperature in Celsius. Therefore it is an one step conversion.

To convert temperature in Fahrenheit scale, we have to first multi given temperature in Celsius scale with 1.8 and then add 32 with it. Therefore it is a two step process.
Hence a one-step conversion is sufficient to convert a temperature in the Celsius scale into the Kelvin scale, but not into the Fahrenheit scale.