SN4 ""

No	Pattern	Freq
1	it is [adv] [adj] for	890
2	it is [adv] [adj] for	840
3	it is [adv] [verb] for	127
4	it is [adv] possible for	99
5	it is [adv] possible for	99
6	it is [adv] [vb pp] for	98
7	it is [adv] important for	77
8	it is [adv] important for	77
9	it is [adv] difficult for	75
10	it is [adv] difficult for	75
11	it is [adv] easy for	53
12	it is [adv] common for	40
13	it is [adv] common for	40
14	it is [adv] [adj -er] for	38
15	it is [adv] easy for	35
16	it is [adv] impossible for	34
17	it is [adv] impossible for	34
18	it is [adv] [adv] for	29
19	it is [adv] rare for	29
20	it is [adv] rare for	28
21	it is [adv] use for	27
22	it is [adv] used for	27
23	it is [adv] [v-ing] for	27
24	it is [adv] necessary for	26
25	it is [adv] necessary for	26
26	it is [adv] [adv] for	23
27	it is [adv] good for	23
28	it is [adv] useful for	19
29	it is [adv] useful for	19
30	it is [adv] essential for	18