逐行用换行符分隔
按正则表达式逐列拆分

rawtxt = """The theory of comparative cost advantage theory was Introduced by----- a) Alfred Marshall b) David Ricardo c) Taussig d) Heberler
The Ricardo’s comparative cost theory is based on which of the following assumption a) Common Market b) Equal cost c) Monopoly d) Free Trade"""

df = pd.DataFrame({"rawtxt":rawtxt.split("\n")})
df.rawtxt.str.split(r"[a-z]\)").apply(pd.Series)

输出

012340比较成本优势理论是由李嘉图·马歇尔·李嘉图·托塔西格伯勒提出的，李嘉图的比较成本理论是基于以下哪一个假设：共同市场平等成本垄断自由贸易

假设您能够从pdf中提取文本，每个句子/问题之间用新行隔开，您可以像这样使用regex：

import re

regex = r"(.+)(a\).+).+(b\).+).+(c\).+).+(d\).+)"
pdf_txt = """The theory of comparative cost advantage theory was Introduced by----- a) Alfred Marshall b) David Ricardo c) Taussig d) Heberler\n 
            The Ricardo’s comparative cost theory is based on which of the following assumption a) Common Market b) Equal cost c) Monopoly d) Free Trade\n"""

matches = re.finditer(regex, pdf_txt, re.MULTILINE)

data = {1 : [], 2 : [], 3 : [], 4 : [], 5 : []}

for match_num, match in enumerate(matches, start=1):
    for group_num in range(0, len(match.groups())):
        data[group_num + 1].append(match.group(group_num + 1))

df = pd.DataFrame(data)
df.columns = ['Question', 'A', "B", "C", "D"]
print(df.head())