Consider the following statements:

Ranking's theory and Coulomb's theory give same values of coefficients of active and passive earth pressure when

1.   the retaining wall has a vertical back.

2.   the backfill is cohesionless.

3.   angle of slope of backfill is equal to the angle of internal friction.

4.   angle of slope of backfill is $0°$

5.   angle of wall friction $\mathrm{\delta } \mathrm{is} 0°$

6.   an