SN4 ""

No	Pattern	Freq
1	it is [adv] difficult [verb]	558
2	it is [adv] difficult [to-vb]	554
3	it is very difficult [verb]	167
4	it is extremely difficult [verb]	64
5	it is often difficult [verb]	59
6	it is more difficult [verb]	57
7	it is [adv] difficult make	25
8	it is [adv] difficult to make	25
9	it is [adv] difficult find	24
10	it is [adv] difficult to find	24
11	it is sometimes difficult [verb]	22
12	it is [adv] difficult see	19
13	it is [adv] difficult to see	19
14	it is always difficult [verb]	18
15	it is also difficult [verb]	16
16	it is [adv] difficult to determine	15
17	it is [adv] difficult determine	15
18	it is [adv] difficult know	14
19	it is [adv] difficult get	14
20	it is [adv] difficult to say	14
21	it is [adv] difficult say	14
22	it is [adv] difficult to know	14
23	it is [adv] difficult establish	13
24	it is [adv] difficult to establish	13
25	it is [adv] difficult to get	13
26	it is [adv] difficult to distinguish	12
27	it is so difficult [verb]	12
28	it is [adv] difficult distinguish	12
29	it is still difficult [verb]	11
30	it is quite difficult [verb]	11