问题：
[单选题]Read the following paragraph, and then answer the questions that follow.
Assignment essay tasks are set to assist students to develop mastery of their study subject. Firstly, assignment tasks enhance understandings about subject matter. Yang and Baker (2005, p. 1) reason that "to master your learning materials and extend your understandings, you need to write about the meanings you gain from your research". Secondly, research (Jinx, 2004; Zapper, 2006) clearly demonstrates that students learn the writing conventions of a subject area while they are researching, reading and writing in their discipline. This activity helps them to "crack the code" of the discipline (Bloggs, 2003, p. 44). Thus, students are learning subject matter and how to write in that disciplinary area by researching and writing assignment essays.
Adapted from: http://learninghub.une.edu.au/tlc/aso/aso-online/academic-writing/academic-paragraphs.php
1. Which is the thesis statement?
AThus, students are learning subject matter and how to write in that disciplinary area by researching and writing assignment essays.
BSecondly, research (Jinx, 2004; Zapper, 2006) clearly demonstrates that students learn the writing conventions of a subject area while they are researching, reading and writing in their discipline.
CAssignment essay tasks are set to assist students to develop mastery of their study subject.
DThis activity helps them to "crack the code" of the discipline (Bloggs, 2003, p. 44).
