¿Por qué se condensó la nube cósmica que originó el sistema solar?

Which one of the following is the correct rhyme to keep in mind when using the spanish counterparts to this, that, those and these? a “this” and “these” both have t’s, “that” and “those” don’tb “that” and “those” both have t’s, “this” and “these” don’tc “that” and “those” both have s’s, “this” and “these” don’td “this” and “these” both have s’s, “that” and “those” don’t

El estudiante leía una novela de terror cuando, de repente, alguien _ a su puerta a. llamé b. llamó c. llamando d. llamaba

Which pair of verbs correctly completes the sentence diego de los estados unidos pero ahora en españa. a. está, es b. es, está c. soy, es d. estoy, está