Correct answer:
cruce
Basically, el cruce means the intersection. So this sentence simply means that the streets meet where they intersect. On the other hand, calles is a feminine plural noun, so you must use the definite articles that also matches this form, which is las. Furthermore, cruzan is the conjugation of the verb cruzar for the third person plural in the simple present. Finally:
Las calles cruzan en el cruce de calles
