Example sentences of "but it is often [adj] [verb] " in BNC.

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1 They fry can be left with the parents until they attain anything up to one inch in length , but it is often advisable to remove the parents long before this .
2 A chance finding , outside the mainstream of scientific research , can sometimes be very valuable , but it is often difficult to see its potential .
3 But it is often difficult to judge .
4 Other places were also hit savagely from time to time , but it is often difficult to tell from the registers which particular disease was responsible for an unusually high number of deaths .
5 By changing the excitation frequency we can probe the upper-state vibrational levels , but it is often difficult to identify the ν'=; 0 level , which may have low probability of excitation or emission .
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