Choose the sentence in which the underlined word is grammatically correct.

A. Africa no está tan grande como Eurasia.
B. Era amigo de la princesa de India.
C. El príncipe está de Sudamérica.
D. El río más grande del mundo es en Sudamérica.

Please list the underlined words.

esta'

era
esta'
es

B. correctly uses a conjugated form of the verb ser.

The others use incorrect choices for ser/estar

The correct sentence is D. "El río más grande del mundo es en Sudamérica."

To determine the correct answer, you need to analyze the grammar and determine if the structure and word choice are accurate.

In option A, the word "grande" is correctly used as an adjective to describe the size of Africa. The comparison is also correct using "tan" to indicate "as" or "so."

In option B, the word "India" is capitalized, indicating a proper noun, which is appropriate for a country. However, it is grammatically incorrect to use the preposition "de" before a proper noun to indicate belonging or origin. Instead, the correct preposition to use is "de" before a common noun, for example, "el amigo de la princesa de la India" (the friend of the princess from India).

In option C, the word "Sudamérica" is a proper noun for South America, and it is correct to use "en" as the preposition to indicate location or position. However, the verb "estar" is more suitable for temporary conditions, while the verb "ser" is used for permanent or inherent characteristics. Therefore, the correct sentence would be "El príncipe es de Sudamérica" (The prince is from South America).

In option D, the word "Sudamérica" is correctly used as a proper noun, and the preposition "en" is appropriately used to indicate the location of the river. The comparative structure "más grande" (largest) is also correctly used to describe the river.

Hence, the sentence that is grammatically correct is option D, "El río más grande del mundo es en Sudamérica."