Multiple Choice, Single Answer (Core)

Read the text and answer the question.

Denny's mobile provider, TalkWave, sent him a text offering to upgrade his plan from 10GB to 25GB of monthly data for an extra $8 a month. The offer also included unlimited weekend calling, which his current plan did not have. To accept, Denny had to reply 'YES' to the text within seven days, after which the new plan would take effect on his next billing cycle automatically. If he ignored the message, his existing plan would simply continue unchanged, with no penalty or automatic upgrade applied. Customers who upgraded could switch back to their original plan once, free of charge, within 30 days.