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, shoddy, goddess, riddance, adduce, addict, addiction, pudding