For protection from frost, concrete should be:
Try it first: pick an option, then read the explanation.
Protecting Concrete from Frost
Frost damage occurs when water in the pores of concrete freezes and expands (by ~9% in volume), generating internal tensile stresses that crack the matrix. All three measures help prevent this:
A — Dense concrete has a low permeability, so less water enters the pore system to begin with.
B — Freedom from cracks means there are fewer pathways for water to penetrate and accumulate.
C — Perfect adhesion between mortar and aggregate prevents the formation of micro-gaps at the interface, which are preferential sites for water accumulation and ice nucleation.
Key takeaway
Frost resistance = dense + crack-free + good aggregate bond. Air entrainment (not listed here) is the modern primary method; this question focuses on the physical requirements.