Which of the following examples best demonstrates transfer by a Spanish speaker who is in the process of acquiring English as a second language?

The example that illustrates transfer from Spanish to English most effectively is the one where the speaker incorrectly applies a rule of Spanish syntax in the sentence "I have a pen blue." In Spanish, adjectives typically follow the nouns they describe (e.g., "una pluma azul" translates to "a pen blue"). This structure is a clear case of language transfer, as the speaker relies on the syntax rules of their native language rather than adhering to the rules of English, where adjectives generally precede the nouns they modify (e.g., "a blue pen"). This demonstrates how linguistic features from the speaker's first language can influence their use of the second language, showcasing the process of language acquisition and interference.

The other choices highlight different aspects of language use, such as vocabulary use or grammatical errors that don't necessarily reflect transfer of grammatical structure from Spanish to English.