Final answer:
The past tense verb of 'design' is 'designed', formed by adding '-ed' to the end of the verb.
Step-by-step explanation:
The verb 'design' is a regular verb in English. In general, we form the past tense of regular verbs by adding '-ed' to the end. So, the past tense of 'design' is 'designed'.
Learn more about Past Tense Formation