Question 1005494
a) a/b+c/d=(a+c)/(bd)
This is  incorrect (unless b=1 and d=1) because a/bd 
does not equal a/b and c/bd does not equal c/d
.
b). a/b+c/d=(a+c)/(b+d) 
This is incorrect because you cannot add fractions 
merely by adding numerators and denominators.
.
c).  a/b+c/d=(ad+bc)/(bd)
This is correct:
{{{(a/b)+(c/d)=(ad+bc)/(bd)}}} 
{{{(a/b)(d/d)+(c/d)(b/b)=(ad+bc)/bd}}}
{{{(ad/bd)+(bc/bd)=(ad+bc)/bd}}}
{{{(ad+bc)/bd=(ad+bc)/bd}}}