Indentify the word that has no suffix, and the word whose suffix is different from others.Isolate the suffix that remaining two words share and...

If I understand your question correctly, here is an analysis of each:

A. "Actor" and "rider" have suffixes that mean "one who acts" and "one who rides."  The "er" suffix in "colder" indicates a comparative form, for example: He is colder than I am.  "Silver has no suffix at all.

B. Both "tresses" and "melodies" are plural forms.  "Bess's" is a possessive form, while "guess" has no suffix at all.

C. "Running" and "handling"  share the same suffix, "ing," which place "run" and "handle" in the present tense. "Foundling," while it has an "ing" suffix, too, is different because its suffix makes it mean "one who is found," a noun, as opposed to the "ing" that still maintaines a kind of verb form. "Fling" has no suffix at all.

D. "Witches" and "tables" have suffixes that make them plurals.  The "s" in "calculates" changed the verb to a singular third person, and has no pluralizing function.  "Lens" is  singular word, thus the "s" does has no plural function.