Studying the deepest parts of the ocean is a daunting task. Humans cannot survive the crushing pressure, freezing temperatures, and lack of light that characterize what's called the "abyssal zone Specially designed submarines and robots can explore this realm, but __ highly expensive and limited by technical challenges. Which choice completes the text so that it conforms to the conventions of Standard English? Choose 1 answer: A it is B they are C we are D this is

resposta correta é a opção B) they are.

A frase completa seria: "Studying the deepest parts of the ocean is a daunting task. Humans cannot survive the crushing pressure, freezing temperatures, and lack of light that characterize what's called the "abyssal zone". Specially designed submarines and robots can explore this realm, but they are highly expensive and limited by technical challenges.

A palavra "they" se refere aos submarinos e robôs especialmente projetados para explorar o reino abissal, que são mencionados anteriormente na frase. Portanto, a opção B) "they are" é a que completa o texto de forma coerente e em conformidade com as convenções da língua inglesa padrão.