Final answer:
To complete the sentence with the correct past subjunctive form, it should read: "Mi madre prefería que ellos no mandaran mensajes de texto a sus amigos," where 'mandaran' is the past subjunctive form of the verb 'mandar' for 'they'.
Step-by-step explanation:
The student's question is about constructing sentences in the past subjunctive form of Spanish verbs. The sentence provided by the student is an example where the past subjunctive mood is required to express a hypothetical situation or a wish contrary to reality.
The student is required to complete the sentence so that it reflects what their mother preferred, using the correct past subjunctive form of the verb 'mandar' (to send).The completed sentence should read: "Mi madre prefería que ellos no mandaran mensajes de texto a sus amigos.
" This translates to: "My mother preferred that they not send text messages to their friends."In this case, 'mandaran' is the correct past subjunctive form of the verb 'mandar' for the third person plural (they).