Complete the message with the correct form of ser or estar

Unas son redondas (round), otras ovaladas (oval), unas piensan mucho, otras casi nada. ¿qué es? uno larguito, dos más bajitos, otro chico (small) y flaco (skinny), y otro gordazo (fat). ¿qué son? como la piedra (rock) son duros (hard), para el perro un buen manjar (delicacy) y sin ellos no podrías (you couldn't) ni saltar (to jump) ni caminar. ¿qué parte del cuerpo describe? juntos vienen, juntos van, uno va delante, otro va atrás (behind). ¿qué son?

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

What is the imperfect past tense of lento (slow) and barstow ( cheap ) ?