Answer:
Tu
Step-by-step explanation:
The possessive adjective that best completes the sentence "¿Es nueva ______ bicicleta?" is "tu". This is the correct form of the possessive adjective for "you" (singular informal) in Spanish, and it is used to indicate that the bicycle belongs to you. The other options, "mis" and "sus", are the possessive adjectives for "my" and "their", respectively, and would not be appropriate in this context.