We study hard so that we may get admitted to good universities. 

Choose the option that best corrects the underlined words.  

• The whole meaning of a subordinate sentence ("we may be admitted to good universities") is dependent on the main clause ("We study hard"). 
• A subordinating conjunction is used to join these two sentences together. The subordinate sentence here explains the reason or purpose for which something is done; the reason is 'to get admitted to a good university,' and what is required to achieve this is 'to study hard.' 
• "So that" is a conjunction used in purpose-related sentences, such as the one given; thus, no alteration is required, and option D is valid.
• 'Yet' is a coordinating conjunction that expresses the contrast between two sentences; it joins two separate sentences that do not rely on one other for complete meaning.
• Because the supplied sentence has a dependent clause and no contrast between the clauses, 'yet' cannot be used. Thus, option A is incorrect.
•  ' Because 'but' and 'and' are also coordinating conjunctions and the provided sentence requires subordinating conjunction, alternatives B and C are invalid.

Hence, option D is the correct answer.