PREP1 No.154 & PREP2 No.29 两题求助

PREP1 154.

Some patients who do not respond to therapies for depression may simply have received inadequate treatment, having, for example, been prescribed a drug at a dosage too low to be effective or having been taken off a drug too soon.

(A) having, for example, been prescribed a drug at a dosage too low to be effective or having been

(B) having, for example, a drug prescription that was ineffective because the dosage was too low, or being

(C) as, for example, having too low of a dosage of a prescribed drug for it to be effective, or being

(D) when they have, for example, been prescribed too low a drug dosage to be effective, or were

(E) for example, when they have a drug prescription with a dosage too low to be effective, or been

正确答案A. 语法笔记关于A选项的解释是having been前后平行。但是不管是白勇语法还是PREP语法解释上都说过，完成时的进行时态不能作为分词修饰。如何解释呢

PREP2 29.

Unlike many United States cities, where a river is no longer the focal point of urban life, the river in San Antonio winds through the middle of the business district, and the River Walk, or Paseo del Rio, is the city's most popular attraction.

(A) Unlike many United States cities, where a river is no longer the focal point of urban life, the river in San Antonio

(B) Unlike the river in many cities in the United States, which is no longer the focal point of urban life, in San Antonio the river

(C) Today the river in many cities in the United States is no longer the focal point of urban life, unlike San Antonio, where it

(D) In few United States cities today, a river is the focal point of urban life, but the river in San Antonio

(E) No longer do many cities in the United States have a river as the focal point of urban life, but in San Antonio the river

正确答案是E.但是but前后并不平行。笔记里说but前后不一定平行，但是纵观所有其他题目，but考点都是平行。很疑惑？？

请指点。多谢。

对于第一个，只能说这个貌似公理的说法不对...

第二个 举个例子
The
proposed urban development zones represent not a new principle, but one that
was employed in “Operation Bootstrap” in Puerto Rico.

你说的是这种情况，but 作副词 确实要求平行
但是做连词时就不用了 ，跟and 一样，and 后面一定要跟平行么？不是吧
你可以搜搜but做连词的句子，不拘泥与平行结构

having been 可以做定语修饰么？

第二题明白了。谢谢。