Watching Arden in class during her first months at school, sitting forlornly while the other kids worked in pairs, was difficult.
The database contained more females than males, and matching male pairs was difficult.
Comparisons between the different pairs are difficult to make, and shift according to where we stand, the ambient lighting and time of day.
Unique orthologous gene pairs are difficult to identify using standard similarity searches, as multiple candidate genes are typically obtained.
The DoM estimator allows for more straightforward modeling of additional unmatchable covariates and is easier to apply when matched pairs are difficult to select or impute.
Unfortunately, aptamer pairs are difficult to generate, primarily because conventional selection methods preferentially yield aptamers that recognize a dominant "hot spot" epitope.
It is relevant to mention here that sequence-based prediction of kinase-cyclin pairs is difficult: for example, PfPK5, a clear CDK1-3 orthologue, is unexpectedly activated very efficiently in vitro by human cyclin H (a CDK7 activator) and p25 (a highly specific CDK5 activator), among other cyclin-related proteins [ 50].
Another pair which was difficult to differentiate was microorganism versus organism.
Several teachers commented that pairing students fairly was difficult, as students' proficiency levels varied within a given class.
In fairness to Wales, Bale and Ramsey were far from the only players absent from Coleman's preferred starting XI but there is no escaping the extent to which they depend on that pair and it was difficult to see where the equaliser was going to come from until McAuley's error of judgment presented Church with the chance to register his third international goal.
In the other two pairs, the cup size was difficult to estimate because of diffuse pallor.
