A simple way to remember the eight land capability classes is to split them into two groups. Classes I, II, III and IV can grow regular field crops, with class I needing almost no special care and class IV needing very careful management with conservation practices. Classes V, VI, VII and VIII cannot be safely cultivated with ordinary crops at all.
Within that second group, class V land is often nearly flat but blocked from cultivation by some other permanent problem, so it is kept as permanent pasture, range or woodland. Class VI carries a real slope or erosion hazard and is described in the classification tables as land suited to grazing and forestry rather than cultivation. Class VII needs even more caution and supports only light grazing or forestry, and class VIII is fit for nothing beyond wildlife habitat or recreation.
Since the question asks specifically which classes are described as suited for pasture, and class III and class IV are still cultivable classes, the cultivable options can be ruled out. Class V and class VI are the pair the classification system actually names for pasture and grazing use.
\[\boxed{\text{Option 4: class V and class VI}}\]