Which of these pairs contains an inflectional suffix?

The correct answer is the pair that includes the inflectional suffixes -ing and -er. Inflectional suffixes are used to modify a word's tense, number, aspect, or case without changing its part of speech.

The suffix -ing is typically used to form the present participle of verbs, indicating ongoing action (e.g., "running," "singing"). The suffix -er is commonly used to form a comparative adjective (e.g., "taller," "faster") or to indicate someone who performs a specific action (e.g., "teacher," "runner"). Both of these suffixes illustrate how inflection modifies the meaning of the base word while keeping its original grammatical category intact.

In contrast, the other options consist of either phrases (as in the first choice), base nouns (the third option), or verbs in their base form (the last option), none of which demonstrate the use of inflectional morphemes that alter the grammatical function of a word.