The IQ is the ratio of “mental age” to chronological age times 100, with 100 30 the average.
答案：(D) being
【句型】with + O + V-ing 獨立分詞構句（表附帶狀況），「以100作為平均值」；is／are（限定動詞，不能這樣接在with+受詞後面）、been（過去分詞，這個結構需要being不是been）都不合。
看到 with 100 ______ the average，你會覺得這裡缺一個動詞，於是挑了 is 或 are。這是最常見的失分點：把 with 帶出來的這一塊誤當成一個獨立的句子。
先看整句的主結構。The IQ is the ratio of “mental age” to chronological age times 100 本身已經是完整的句子，主詞 The IQ、動詞 is 都齊了。逗號後面的 with 100 ______ the average 是附加上去補充說明的，裡面不能再有一個限定動詞。is 與 are 都是限定動詞，代進去等於一句話出現兩個主要動詞，先出局。這個結構是課本長教的：with 加受詞加受詞補語（表附帶狀態）。受詞是 100，受詞補語就是空格這一塊，用來說明 100 處於什麼狀態。補語位置若要用動詞，必須改成分詞：主動用現在分詞，被動用過去分詞。100 是「作為」平均值，屬主動，所以用 being。還原成完整子句驗算：with 100 being the average 等於 and 100 is the average（而 100 就是那個平均值）。這個句型你在課本看過很多次：with his eyes closed（閉著眼睛，被動，用過去分詞）、with the engine running（引擎還開著，主動，用現在分詞）。本題屬於後者。最後用下一句驗算：an 8-year-old who passes the 10-year-old's test would have an IQ of 10/8 times 100, or 125，10 除以 8 再乘以 100 得 125，高於 100，正說明 100 是那個當作基準的平均值。
is、are：都是限定動詞，with 引導的附帶結構裡不能放限定動詞；何況若真要當成一個句子，前面還缺一個連接詞。been：過去分詞，前面必須有 have 或 has 才能構成完成式，不能單獨放在受詞補語的位置；而且 100 與 the average 之間是主動關係，不是被動。
with one's eyes closed（閉著眼睛）、with the engine running（引擎還開著）、with one's arms folded（雙臂交叉）、the ratio of A to B（A 與 B 的比例）、chronological age（實足年齡）、on average（平均而言）。
French psychologist Alfred Binet (1859-1911) took a different approach from most other psychologists of his day: He was interested in the workings of the 26 mind rather than the nature of mental illness. He wanted to find a way to measure the ability to think and reason, apart from education in any particular field.
In 1905 he developed a test in which he 27 children do tasks such as follow commands, copy patterns, name objects, and put things in order or arrange them properly. He later created a standard of measuring children's intelligence 28 the data he had collected from the French children he studied. If 70 percent of 8-year-olds could pass a particular test, then 29 on the test represented an 8-year-old's level of intelligence.
From Binet's work, the phrase "intelligence quotient" ("IQ") entered the English vocabulary. The IQ is the ratio of "mental age" to chronological age times 100, with 100 30 the average. So, an 8-year-old who passes the 10-year-old's test would have an IQ of 10/8 times 100, or 125.