If we 30 surrounded by an unending abundance of diamonds, we probably wouldn't value them very much.
答案：(D) were
第二型假設語氣（與現在事實相反），If子句用過去式 were（be動詞在假設語氣中不分人稱都用were），主要子句用wouldn't value；be（原形動詞，不合假設語氣時態）、being（現在分詞）、to be（不定詞）都不合。
If 一出現，很多人直覺想到「條件句用現在式」，就挑了原形 be；也有人看到 surrounded 是過去分詞，想再補一個 being 湊出被動。真正的關卡是：這裡的 If 講的不是有可能發生的條件，而是與現在事實相反的假設。
先看主要子句：we probably wouldn’t value them very much，用的是 would 加原形動詞——這是與現在事實相反的假設語氣的標準組合。主要子句一旦出現 would、could、might 加原形，If 子句就要用過去式。語意也對得上：現實是鑽石很稀有（前一段整段都在講 limited in supply），所以「身邊有取之不盡的鑽石」是與現在事實相反的想像。接著是這一題真正的考點：假設語氣的 be 動詞不分人稱一律用 were。課本反覆強調的那一句就是最好的掛鉤——If I were you...（如果我是你…），不寫 If I was you。本句主詞是 we，用 were 也剛好符合一般文法。最後確認形式：空格後面的 surrounded 是過去分詞，were surrounded 合起來是被動語態「被…包圍」，整句是「如果我們被取之不盡的鑽石包圍著」。
be：原形動詞，If 子句需要有時態的動詞，原形不能單獨用。being：現在分詞，不能當子句的主要動詞。to be：不定詞，同樣不能當主要動詞，If 後面要接的是完整的子句。
If I were you（如果我是你）、an abundance of（大量的、豐富的…）、be surrounded by（被…包圍）、value something（珍視某物）、find use for something（覺得某物有用處）、carry a monetary value（具有金錢價值）。
Which is more valuable? Water or diamonds? Water is more useful to mankind than diamonds, and yet 26 are costlier. Why? Called the diamond-water paradox, this is a classic problem posed to students of economics.
The answer has to do with supply and demand. Being a rare natural resource, diamonds are 27 in supply. However, their demand is high because many people buy them to tell the world that they have money, 28 as conspicuous consumption in economics. In other words, the scarcity of goods is 29 causes humans to attribute value. If we 30 surrounded by an unending abundance of diamonds, we probably wouldn't value them very much.
Hence, diamonds carry a higher monetary value than water, even though we find more use for water.