Final answer:
Jazz music's influence on Jack Kerouac's writing is reflected in his prose's rhythm and improvisation, while a counterclaim to the argument presented might suggest literature could evolve independently of jazz or political influences. Identifying informal English in Amy Tan's essay requires an example not provided here.
Step-by-step explanation:
To address the first question regarding Jack Kerouac's writing style influenced by jazz music, we can refer to the phrase 'formalism and align it more closely with the improvisatory musical solos of jazz' from the provided excerpt. This phrase underlines how jazz's rhythm and improvisation permeated Kerouac's literary technique, mirroring the free-flowing and dynamic nature of his prose.
For the second question, which asks for a counterclaim to the provided excerpt, it would be a statement that contradicts or challenges the main argument presented. In this case, a counterclaim might posit that despite the impact of political climate and jazz culture on the writing of the era, literature could have developed its form and thematics independently of these influences.
Regarding the third question on informal English usage in Amy Tan's essay 'Mother Tongue,' no exact excerpt is provided to identify the phrase. However, informal English typically involves colloquial expressions, contractions, and more conversational language that may stand out in an academic essay.