Could triangle abc be congruent to triangle adc by sss? explain.
a. yes but only if ab ~=dc
b. yes but only if bc~= dc
c. no, because ab is not congruent to ac
d. no, because ab ~= da

Having a certain triangle there are some cases of congruency:
SSS (side side side) All three corresponding sides are equal in length.
SAS (side angle side) A pair of corresponding sides and the included angle are equal.
ASA (angle side angle)
AAS (angle angle side)

As we can observe there must be always 3 components of congruency. Triangle ABC can be congruent to triangle ADC by SSS if we have 3 sides that are equal. We already have two components: AB=AD and AC=AC (AC is a common side) so we need the third component BC=CD. The answer to your question is option B.