Apple Inc. opened its first retail store in $2001$ in McLean, Virginia. Until then, its products had largely been sold through other retailers $($e$.$g$.$ Best Buy, Circuit City, CompUSA$).$ By building and operating its first mall$-$based retail stores, Apple was engaging in:

Total quality management $($TQM$)$

Backward vertical integration

Horizontal integration

Outsourcing

Forward vertical integration