SN4 ""

No	Pattern	Freq
1	[verb] [pers pn] twenty years	9
2	[pers pn] [be] twenty years	33
3	[pers pn] be twenty years	33
4	[pers pn] [verb] twenty years	25
5	[pers pn] [was/were] twenty years	22
6	[pers pn] [vb past] twenty years	16
7	[pers pn] [prep] twenty years	14
8	[pers pn] [prep] twenty years	14
9	[pers pn] was twenty years	14
10	[pers pn] for twenty years	11
11	[pers pn] for twenty years	11
12	[pers pn] were twenty years	8
13	[pers pn] [is] twenty years	6
14	[pers pn] [vb base] twenty years	6
15	[pers pn] [am/are] twenty years	5
16	[pers pn] 's twenty years	5
17	[pers pn] [adj] twenty years	5
18	[pers pn] twenty years [adv]	7
19	[pers pn] twenty years [adv]	7