SN4 ""

No	Pattern	Freq
1	it is [adv] difficult [to-vb]	554
2	it is very difficult [verb]	167
3	it is extremely difficult [verb]	64
4	it is often difficult [verb]	59
5	it is more difficult [verb]	57
6	it is [adv] difficult make	25
7	it is [adv] difficult to make	25
8	it is [adv] difficult find	24
9	it is [adv] difficult to find	24
10	it is sometimes difficult [verb]	22
11	it is [adv] difficult see	19
12	it is [adv] difficult to see	19
13	it is always difficult [verb]	18
14	it is also difficult [verb]	16
15	it is [adv] difficult determine	15
16	it is [adv] difficult to determine	15
17	it is [adv] difficult know	14
18	it is [adv] difficult to know	14
19	it is [adv] difficult say	14
20	it is [adv] difficult get	14
21	it is [adv] difficult to say	14
22	it is [adv] difficult establish	13
23	it is [adv] difficult to get	13
24	it is [adv] difficult to establish	13
25	it is so difficult [verb]	12
26	it is [adv] difficult to distinguish	12
27	it is [adv] difficult distinguish	12
28	it is quite difficult [verb]	11
29	it is still difficult [verb]	11
30	it is [adv] difficult to assess	11