Select the option that is related to the fifth number - letter cluster in the same way as the fourth number - letter cluster is related to the third number - letter cluster, and the second number - letter cluster is related to the first number - letter cluster.
ELECTRON : TRONCELE :: FUNCTION : TIONCNUF :: CLUSTERS : ?
1
TERSSUCL
2
TRESSULC
3
TERSSULC
4
TERSUSLC