SN4 ""

No	Pattern	Freq
1	must have been [verb]	793
2	must have been [adj]	760
3	must have been [art]	632
4	must have been [art]	632
5	must have been [adv]	576
6	must have been [adj]	551
7	must have been [adv]	535
8	must have been [vb pp]	496
9	must have been a	481
10	must have been a	430
11	must have been [prep]	294
12	must have been [prep]	294
13	must have been [v-ing]	289
14	must have been the	147
15	must have been the	147
16	must have been [noun]	120
17	must have been [num]	98
18	must have been [det]	93
19	must have been in	89
20	must have been in	89
21	must have been [pron]	89
22	must have been very	71
23	must have been very	71
24	must have been [indef pn]	55
25	must have been an	51
26	must have been [noun sg]	47
27	must have been about	47
28	must have been about	45
29	must have been some	43
30	must have been [noun prp]	43