The thesis statement that the author will attempt to prove in the essay is A. Research indicates that there were two main causes for the Titanic disaster: human error and design defects.
The thesis statement is a sentence in which the author summarizes the main idea of an essay, that is to say, what is the topic that will be developed in the piece of writing. In this introduction, the thesis statement is sentence A since it mentions that the Titanic sinking occurred for two main causes. Consequently, what the reader expects from the essay is to be provided with more information about these causes, meaning that the body of the essay will develop this topic with supporting ideas.