In 1990, California native and researcher Ellen Ochoa left her position as chief of the Intelligent Systems Technology Branch at a NASA research center the space agency's astronaut training program. Which choice completes the text so that it conforms to the conventions of Standard English? Choose 1 answer: (A) to join (B) is joining (C) joined (D) joins

To determine the correct choice that completes the sentence in a way that conforms to the conventions of Standard English, we need to analyze the structure of the sentence. The sentence reads: "In 1990, California native and researcher Ellen Ochoa left her position as chief of the Intelligent Systems Technology Branch at a NASA research center ___ the space agency's astronaut training program." The phrase "left her position" indicates that the action took place in the past. Therefore, we need a verb form that matches this past tense context. Now, let's evaluate the options: (A) to join - This is an infinitive form and does not match the past tense context. (B) is joining - This is present continuous and does not fit the past context. (C) joined - This is the simple past tense, which fits the context perfectly. (D) joins - This is present tense and does not fit the past context. The correct choice is (C) joined, as it maintains the past tense consistent with "left." So, the completed sentence would read: "In 1990, California native and researcher Ellen Ochoa left her position as chief of the Intelligent Systems Technology Branch at a NASA research center joined the space agency's astronaut training program." Thus, the answer is: **(C) joined**.