Final answer:
Line D is the best example of anaphora in Kennedy's “address at Rice University”.
Step-by-step explanation:
The best example of anaphora in Kennedy's “address at Rice University” is line D: “But in this city of Houston, this State of Texas, this country of the United States was not built by those who waited and rested and wished to look behind them. This country was conquered by those who move forwarded - and so will space.” Anaphora is the repetition of a word or phrase at the beginning of successive clauses or sentences, and in this line, “this” is repeated to create emphasis and rhythm.