Here are the answers to your questions:
Question 13: Mis dos amigas, Fabiola y Virginia, son muy estudiosas.
Question 14: The best place to put the adjective "perezoso" in the sentence would be at position 3: Diego (1) es (2) un (3) chico (4) perezoso.
Question 15: The theory developed based on observations made on the Galápagos islands is natural selection.
Question 16: The correct way to say "the messy female friend" in Spanish is la amiga desordenada.
Question 17: One of the main tourist attractions in La Habana is El Paseo del Prado.
Question 18: The statement that best describes salsa music is a combination of jazz and Afro-Cuban rhythms.
Question 19: The artistic movement that Pablo Picasso cofound along with Georges Braque is cubism.
Question 20: The artist whose work includes plump and bloated people and animals as a signature feature is Fernando Botero.
If you need any further assistance, feel free to ask!