SN4 ""

No	Pattern	Freq
1	it is [adj] [to-vb] the [noun sg]	1088
2	it is [adj] [to-vb] the [noun pl]	279
3	it is possible [to-vb] the [noun]	245
4	it is difficult [to-vb] the [noun]	189
5	it is important [to-vb] the [noun]	174
6	it is necessary [to-vb] the [noun]	154
7	it is hard [to-vb] the [noun]	74
8	it is easy [to-vb] the [noun]	73
9	it is impossible [to-vb] the [noun]	69
10	it is [adj] to consider the [noun]	52
11	it is [adj] to see the [noun]	44
12	it is [adj] [to-vb] the conclusion	38
13	it is [adj] [to-vb] the conclusion	38
14	it is essential [to-vb] the [noun]	37
15	it is [adj] to understand the [noun]	35
16	it is [adj] to use the [noun]	32
17	it is [adj] to avoid the [noun]	30
18	it is [adj] to assess the [noun]	28
19	it is [adj] [to-vb] the extent	28
20	it is [adj] [to-vb] the extent	28
21	it is interesting [to-vb] the [noun]	24
22	it is [adj] to identify the [noun]	24
23	it is [adj] [to-vb] the effect	23
24	it is [adj] to compare the [noun]	23
25	it is [adj] to examine the [noun]	22
26	it is useful [to-vb] the [noun]	20
27	it is advisable [to-vb] the [noun]	20
28	it is convenient [to-vb] the [noun]	20
29	it is [adj] to imagine the [noun]	19
30	it is [adj] [to-vb] the difference	18