SN4 ""

No	Pattern	Freq
1	it is [adv] [adj] for	1269
2	it is [adv] [adj] for	1219
3	it is [adv] [verb] for	151
4	it is [adv] possible for	144
5	it is [adv] possible for	144
6	it is [adv] [vb pp] for	118
7	it is [adv] easy for	79
8	it is [adv] difficult for	78
9	it is [adv] difficult for	78
10	it is [adv] important for	77
11	it is [adv] important for	77
12	it is [adv] [adv] for	67
13	it is [adv] necessary for	66
14	it is [adv] necessary for	66
15	it is [adv] easy for	61
16	it is [adv] [adv] for	61
17	it is [adv] unusual for	58
18	it is [adv] unusual for	58
19	it is [adv] uncommon for	55
20	it is [adv] uncommon for	55
21	it is [adv] common for	41
22	it is [adv] common for	41
23	it is [adv] impossible for	38
24	it is [adv] impossible for	38
25	it is [adv] [adj -er] for	38
26	it is [adv] unknown for	37
27	it is [adv] unknown for	37
28	it is [adv] good for	34
29	it is [adv] [v-ing] for	31
30	it is [adv] rare for	30