What is the singular form of estos libros

Okay so i'm taking an online spanish course (penn foster), and in the study guide, you have to create a bunch of sentences with words you've learned so far. translating, reading, and those kinds of things are fairly easy, but when it comes to making my own sentences, my brain just kinda waltz's away. anyone got any tips?

Which of the following is a common subject of teodor núñez ureta's paintings? a. andean peasants b. cuzco city life c. traditional peruvian food d. the spanish conquest of the incas

Good evening can you me a partir de estas palabras redacta una resume: el aumento la temperatura la extensión de nuestra flora y funa las emisiones mondiales peru 1% cambio climatico planeta las zonas rurales 50% la intensidad energetica del consumo de lena el calentamiento global energia renovables o no renovables emisiones de gases de efecto ionvernadero la yareta energia solar, éolica ,nuclear contaminante los combustibles fosiles lena carbon atmosfera retenga la energia acumulada los pais vulnerables del mundo la escasez del agua la perdida de cultivos energia de la biomasa (vegetacion) energia hidraulica (embalses) energia geothermica la bosta producen de dioxide de carbon humanidad