Consider the following statements:

Blow down is necessary on boilers, because 1. the boiler water level is lowered rapidly in case it accidentally rises too high.

2. the precipitated sediment of sludge is removed while the boiler is in service.

3. the concentration of suspended solids in the boiler is controlled.

Of these statements

(a) 1,2 and 3 are correct

(b) 1 and 2 are correct

(c) 3 alone is correct

(d) 1 and 3 are correct