¿Qué signo de puntuación señala cosas que el informante expresa?

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 these words best completes the first sentence? el clima de invierno es y cae nieve. por eso es posible ir a esquiar. a. nieve b. frío c. templado d. caliente

Decide whether the sentence is grammatically correct or incorrect as written. hay muchos estudiantes en la escuela.