Which of the following pairs is an example of a morpheme?

The pair "un-lady-like" is a clear example of a morpheme because it consists of distinct morphemes that convey specific meanings. A morpheme is the smallest meaningful unit of language, and in this case, "un-" is a prefix that negates the meaning of the root "lady," and "like" functions to relate the concept of being a lady in a particular manner. Together, they form a complete meaning that implies not behaving in a manner typically associated with a lady.

In contrast, the other choices do not illustrate pairs that consist of morphemes as effectively. "Happy" and "sad" are standalone words with clear meanings but do not consist of smaller meaningful units combined together. "Run" and "jump" are also independent words that do not show the construction of morphemes. Lastly, "reading" and "writing," while they are action nouns derived from verbs, do not break down into smaller morphemes within the pair itself; instead, they are simply acts represented by whole words. Thus, the combination of "un-lady-like" distinctly showcases how morphemes can blend together to create new meanings.