SN4 ""

No	Pattern	Freq
1	must [adv] have been	176
2	must [adv] have been	176
3	must [adv] have been	153
4	must also have been	25
5	must also have been	25
6	must not have been	23
7	must [not/n't] have been	23
8	must once have been	22
9	must once have been	22
10	must not have been	19
11	must surely have been	16
12	must surely have been	16
13	must already have been	15
14	must already have been	15
15	must therefore have been	10
16	must therefore have been	10
17	must always have been	9
18	must always have been	9
19	must often have been	7
20	must often have been	7
21	must still have been	7
22	must still have been	7
23	must certainly have been	5
24	must certainly have been	5