核酸分子中百分比含量相对恒定的元素是
A．碳(C)B．氢(H)C．氧(O)D．氮(N)E．磷(P)
参考答案：E
_______ jeans were invented over 100 years ago, they're still in fashion today.
A．Because
B．If
C．Although
D．Since
工程上主要采用哪些方法除去或减少液体电介质中杂质的影响？
