定语从句在说明文中的运用 — 英语填空题
题目
完成下列句子，填入适当的定语从句引导词：1) The telescope, ___ lens has been polished for three years, will capture distant galaxies. 2) Astronauts face challenges ___ ordinary people can hardly imagine. 3) The Mars probe sent back photos ___ show traces of ancient rivers.