Explanation:

To convert a sentence from Simple Present Tense ('rushes') to Simple Past Tense, the verb needs to be changed to its past simple form. The past simple of 'rushes' is 'rushed'. Option A uses past perfect ('had rushed'). Option C uses past continuous ('was rushing'). Option D uses present continuous ('is rushing') and is also a duplicate/malformed option. Therefore, 'Sohrab rushed forward to help the old lady cross the road' is the correct simple past tense conversion.