SN4 ""

No	Pattern	Freq
1	it is [adv] necessary [verb]	461
2	it is [adv] necessary [to-vb]	460
3	it is [adv] necessary [verb]	286
4	it is not necessary [verb]	175
5	it is [not/n't] necessary [verb]	175
6	it is not necessary [verb]	167
7	it is also necessary [verb]	50
8	it is also necessary [verb]	50
9	it is only necessary [verb]	37
10	it is only necessary [verb]	37
11	it is therefore necessary [verb]	33
12	it is therefore necessary [verb]	33
13	it is now necessary [verb]	23
14	it is now necessary [verb]	23
15	it is [adv] necessary consider	22
16	it is [adv] necessary to consider	22
17	it is often necessary [verb]	21
18	it is often necessary [verb]	21
19	it is still necessary [verb]	17
20	it is still necessary [verb]	17
21	it is [adv] necessary have	16
22	it is [adv] necessary to have	16
23	it is then necessary [verb]	14
24	it is then necessary [verb]	14
25	it is [adv] necessary to use	13
26	it is [adv] necessary use	13
27	it is usually necessary [verb]	12
28	it is usually necessary [verb]	12
29	it is [adv] necessary to know	10
30	it is [adv] necessary examine	10