(c) heart
'Lub-dup' sound is produced due to the action of the heart.
The "lub" is the first heart sound which is commonly termed S1.
It is caused by the disturbance caused by the closure of mitral and tricuspid valves at the start of systole.
The second sound is "dub" which is commonly termed S2.
It is caused by the closure of aortic and pulmonic valves which marks the end of systole.
