SN4 ""

No	Pattern	Freq
1	[adv] once a	340
2	[noun] once a	305
3	[adv] once a	300
4	be once a	227
5	[be] once a	227
6	[was/were] once a	214
7	[noun sg] once a	211
8	was once a	201
9	[verb] once a	199
10	[conj] once a	132
11	least once a	117
12	least once a	117
13	[prep] once a	87
14	[prep] once a	87
15	[pron] once a	64
16	[vb pp] once a	64
17	[noun pl] once a	63
18	[coord] once a	60
19	[pers pn] once a	54
20	at once a	54
21	at once a	54
22	only once a	52
23	only once a	52
24	[subord] once a	50
25	about once a	39
26	about once a	39
27	[vb base] once a	38
28	[adv prt] once a	35
29	than once a	33
30	than once a	33