dilemma [di- = two 二；lemma= premise 假设=>“a choice between two premises在两种假设之间选择”→]n. difficult choice between two undesirable things 窘境，进退两难 / Her dilemma was whether to marry Paul, who was poor, or Charles, who was ugly. 使她左右为难的是，嫁给穷光蛋保罗呢，还是嫁给丑八怪查尔斯。

由di-开头的术语为数不少，这里举3个例子说明。

dioxide [di- = two二; oxide n. 氧化物→] n. an oxide having two atoms of oxygen for each molecule 二氧化物 / Things can not burn in carbon dioxide.东西不能在二氧化碳中燃烧。

divalent [di- = two 二； valent a. 化学价的→]a. having a valence of two; bivalent 二价的 / Oxygen is a divalent element.氧是一种二价的元素。

diatomic [di- = two 二； atom n. 原子；-ic a. = having 有… →]a. having two atoms in each molecule 双原子的 / Oxygen molecule is diatomic. 氧分子是含双原子的。