The subject of the sentence (the writing, which is singular) does not agree with the pronoun (they, which is plural and needs to be replaced by the singular it).
It is important to avoid wordy or unduly long phrases such as due to the fact that or for the reason that and instead use a shorter word like because.
A. The subject of the sentence (the writing, which is singular) does not agree with the pronoun (they, which is plural)
B. due to the fact that is wordy and can be replaced by because
C. the pronoun their, which is plural, does not agree with the subject the writing, which is singular; the phrase is awkward and long,br/> D. the subject of the sentence (the writing) agrees with the pronoun (it); because is concise
E. the phrase for the reason that is wordy and can be replaced by the single wordbecause

There are three main issues being tested in this question.
(1) The phrase their home is redundant as the word their could be eliminated
(2) The phrase other tribal groups historically experienced (with its verb in the simple past tense) must be replaced with a phrase that uses the past perfect tense (i.e., historically had experienced). The past perfect tense must be used since we are dealing with two actions in the past where one action came before another (i.e., the historic ability to find food predated the decision to move). The word historically makes it clear that the ability to find food referred to the period of time before the individuals decided to move in 2007.
(3) The word less cannot be used with difficulties since difficulties can be counted and the proper word for countable items is fewer
A. the word their is redundant; the word less should be replaced by the word fewer; the simple past tense (experienced) should be replaced by the past perfect tense (had experienced)
B. the simple past tense (experienced) should be replaced by the past perfect tense (had experienced)
C. the word their is redundant; the simple past tense (experienced) should be replaced by the past perfect tense (had experienced)
D. many indigenous people...left home not in search of other tribal groups (as this option incorrectly states), but for land where other tribal groups historically had experienced fewer difficulties finding food
E. the unnecessary word their is properly eliminated; the past perfect tense is correctly used; the word fewer is used with countable items

The current sentence uses the incorrect idiom to credit x ... for y. The correct idiom is to credit x ... with y
A. to credit x ... for y is not the correct idiom
B. having propelled is not the proper verb tense and should be replaced with propelling
C. to credit x ... as y is not the correct idiom
D. to credit x ... to y is not the correct idiom
E. to credit x ... with y is the correct idiom; propelling instead of having propelled is also correct

There are two main problems with the original sentence.
(1) The subject of this sentence (financial problems) is plural and does not agree with the verb (ranks), which is singular. Do not be thrown off by the appositive between the subject and verb that is designed to confuse you.
(2) The phrase rank as one of the high causes is not idiomatically correct. Instead, itemsrank as one of the leading causes.
A. The subject (which is plural) and verb (which is singular) do not agree; ranks as one of the high causes is awkward and unidiomatic
B. This sentence correctly uses a plural verb with its plural subject; the concise and idiomatically correct phrase rank as one of the leading causes is used
C. The phrase rank as one of the most high causes is awkward, unidiomatic, and redundant (the words most and high convey the same idea)
D. The subject (which is plural) and verb (which is singular) do not agree
E. The phrase rank as one of the most leading causes is awkward, unidiomatic, and redundant (the words most and leading convey the same idea)