Sentence structure -
In recent years, many prominent consumer goods retailers have increasingly invested in Mandarin-language marketing,
in part that their Chinese branches should acquire new customers and
partly because the Chinese Diaspora is projected to increase substantially over the next decade.
Parallelism is being tested. In the second part after and we have "partly" so in the first part also we need "partly"
Meaning -
Many prominent consumer good retailers have increasingly invested in Mandarin-language marketing for the following reasons-
1. Chinese branches to acquire new customers
2. the Chinese Diaspora is projected to increase substantially over the next decade
(A) in part that their Chinese branches should acquire new customers
Incorrect. Not parallel. Meaning changed due to "should". Increase in marketing is done to acquire new customers for Chinese branches
(B) in part for the acquisition of new customers by their Chinese branches
Incorrect. Not parallel
(C) partly because of their Chinese branches acquiring new customers
Incorrect. Meaning changed - Increase in marketing is done to acquire new customers for Chinese branches
(D) partly to acquire new customers for their Chinese branches
Correct.
(E) partly because new customers should be acquired by their Chinese branches
Incorrect. Meaning changed due to "should". Increase in marketing is done to acquire new customers for Chinese branches
D is the correct answer