dd addition 加, 加法 [Card #1; 字卡第1張: 第3個單字, 字母組合發音 dd]
dd = /d/(2個相同子音在一起, 只發一個音)

Some more examples(更多例字):add, odd, oddity, paddle, saddle, waddle, straddle, meddle, peddle, needle, diddle, fiddle, middle, piddle, riddle, griddle, twiddle, coddle, toddle, toddler, cuddle, huddle, muddle, puddle, befuddle, ladder, bladder, fodder, rudder, shudder, sudden, hidden, caddy, eddy, buddy, muddy, ruddy, goddess, riddance, addict, addiction, pudding