SN4 ""

No	Pattern	Freq
1	[conj] it is [to-vb] in	11
2	[subord] it is [to-vb] in	10
3	if it is [to-vb] in	9
4	if it is [to-vb] in	9
5	it is [adj] [to-vb] in	220
6	it is [adj] [to-vb] in	209
7	it is important [to-vb] in	42
8	it is important [to-vb] in	42
9	it is [verb] [to-vb] in	30
10	it is possible [to-vb] in	28
11	it is possible [to-vb] in	28
12	it is necessary [to-vb] in	27
13	it is necessary [to-vb] in	27
14	it is [vb pp] [to-vb] in	22
15	it is impossible [to-vb] in	11
16	it is impossible [to-vb] in	11
17	it is difficult [to-vb] in	11
18	it is difficult [to-vb] in	11
19	it is likely [to-vb] in	9
20	it is likely [to-vb] in	9
21	it is [v-ing] [to-vb] in	8
22	it is easy [to-vb] in	8
23	it is useful [to-vb] in	6
24	it is essential [to-vb] in	6
25	it is [adj -er] [to-vb] in	6
26	it is useful [to-vb] in	6
27	it is essential [to-vb] in	6
28	it is expect [to-vb] in	5
29	it is [noun] [to-vb] in	5
30	it is [adj -est] [to-vb] in	5