A direct object is a noun that denotes the <u>recipient</u> of the action of a verb.
In the sentence 'Which mission did Sally Ride fly for NASA?', the word mission is the recipient of the action of the verb fly (used together with the helping verb did to show that this action happened in the past.)
SAME MY FREAKIN TEACHER IS MAKING ME ANSWER A BUNCH OF QUESTIONS FROM THE STUPID BOOK AS IF WE DONT ALREADY HAVE ENOUGH GOING ON IN OUR LIVES BECAUSE OF THE DUMB VIRUS