If a child is to develop healthy bones, the child’s diet must include

Original argument:
If a child is to develop healthy bones, the child’s diet must include sufficient calcium.
It therefore follows that the diets of children who do not develop healthy bones do not include sufficient calcium.

It says that enough calcium is necessary for healthy bones (A is necessary for B)
So no healthy bones means the child did not get enough calcium (So no B means no A)

This reasoning is flawed. A is necessary for B so if A is not there, B will not happen. But if B did not happen, that does not mean that A wasn't there. Perhaps healthy bones need Vit D as well which was not there in the diet though the diet had enough calcium and that is why the child doesn't have healthy bones.

Original logic:
A is necessary for B
So no B means no A

(A) If bread is to have a firm crust, it must be baked at the right temperature. It therefore follows that bread that is not baked at the right temperature will not have a firm crust.

Right temp is necessary for firm crust.
So if not at right temp, will not have firm crust.

This logic is correct. Since right temp is necessary for firm crust, without right temp, there will not be firm crust. This becomes:
A is necessary for B
So no A means no B
Not same as our original logic.

(B) A cake must contain the right amount of flour in order to taste good. It therefore follows that cakes that do not taste good do not contain the right amount of flour.

Right amount of flour is necessary to taste good.
If 'not taste good', 'not right amount of flour'.

This translates to
A is necessary for B
So no B means no A
This is the same logic as our original logic. It is also flawed just like our original logic.

Answer (B)

Hi Karishma

Can you please elaborate the flaws with C. Why it cant be the answer.