| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [noun] of [v-ing] [noun] [noun pl] | 846 |
|
| 2 | difficulty [prep] [v-ing] [noun] [noun pl] | 39 |
|
| 3 | difficulty of [v-ing] [noun] [noun] | 28 |
|
| 4 | difficulty of [verb] [noun] [noun pl] | 17 |
|
