Because it is so hard to acquire sufficient telescope time for a sky survey, SETI observations at Arecibo were conducted up to now in the in the piggy-back mode.是什么意思_Because it is so hard to acquire sufficient telescope time for a sky survey, SETI observations at Arecibo were conducted up to now in the in the piggy-back mode.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句