Many experts in the field believe that future phones will not only look very different---they may not even be 11.
答案：(D) seen
seen（被看見）呼應下文 They may be hidden in jewelry or accessories, or even embedded in the body（可能藏在珠寶配件中，甚至被植入體內），表示未來手機可能連被看見都很難；heard／sold／changed 均不符合此處語境。
四個選項都是過去分詞，形態一樣，你會挑一個中文讀起來最順的。
鑑別度高達 62，分開的是有沒有接住破折號前後那條線。這是同義勾環：破折號前面是 future phones will not only look very different（未來的手機不只長得很不一樣），關鍵字是 look（看起來）；破折號後面用 not only 的下半段把話再推一步——連「被看到」都不一定。look 與 be seen 講的是同一件事、同一個感官，所以空格填 seen。填進去讀成 they may not even be seen（它們甚至可能不會被看到）。下一句 They may be hidden in jewelry or accessories, or even embedded in the body（可能藏在珠寶或配件裡，甚至嵌進身體）正是在說明為什麼看不到，可以拿來驗算。
heard（被聽到）與手機的關係看似最近，但破折號前講的是外觀，不是聲音；sold（被賣）與 changed（被改變）文法上都放得進去，形態吻合，容易被順手選走，但兩個都接不上「外觀」這條線——手機當然還是會被賣、會被改良，那樣寫 not even 就完全沒有加強的效果。
not only ... but also ...（不只……而且……）、be embedded in（嵌入、植入）、be hidden in（藏在……裡）、additional features（額外的功能）、evolve（演化、發展）、accessories（配件）。
The telephone is widely considered as the most rapidly evolving technological device today. Many experts in the field believe that future phones will not only look very different—they may not even be 11. They may be hidden in jewelry or accessories, or even embedded in the body. They will undoubtedly have a lot of additional features and 12 functions, and users may interact with them in new ways, too.
13 they are still called "phones"—a word meaning "voice" in Greek—making voice calls may no longer be their primary function. With advances in contemporary design and technology, the phones may 14 remote controls, house keys, Game Boys, maps, flashlights, health monitors, recorders, handguns, and so on.
15, they will be "the remote-control for life."