Select the most appropriate option that can substitute the highlighted segment in the given sentence.
We have perhaps never seen an ablest series of advocates than these ten standing in a row.

Correct option is C

The correct substitution of the highlighted words is (C) more able.
#Explanation:# The connector than signals a comparative construction, so the degree must be comparative, not superlative. The phrase “an ablest” is wrong on two counts: (i) ablest is a superlative (should pair with the and typically with of/in/that, not than), and (ii) the article an cannot precede a superlative; superlatives take the. Replacing the highlighted part with more able correctly aligns with than. (Stylistically, the fully corrected sentence would read “a more able series … than …”, but the test asks to substitute only the highlighted segment.)

Grammatical rule used:

Comparative: more/–er + adjective + than → more able/abler than X.

Superlative: the + –est/most + noun → the ablest (of/in/that …); avoid than after a superlative.

Article with degree: Superlatives take the; comparatives may take a/an before the modified noun phrase (a more able series).

Example:

We have never seen a more efficient method than this one.

She is the most diligent student in the class.

Information booster / exceptions:

With shorter adjectives, –er forms are common (abler than), but with adjectives like able, both abler and more able exist; more able is generally preferred in formal usage.

Use superlative only for selection within a set (the ablest of them all), not when directly followed by than.