Sentence examples for are a difficulty from inspiring English sources

The largest studies however (n = 562 & n = 245; [ 29, 30]), originated from South Africa with conflicting results, as mixed ancestry in African populations are a difficulty for genetic investigators.

The low mutation rates and the expansion of the genomes have been explained by the mutational burden hypothesis (Lynch et al. 2006; Lynch 2007), but a few species with both highly expanded genomes and high mutation rates are a difficulty for this hypothesis (Cho et al. 2004; Parkinson et al. 2005; Sloan, Muller, et al. 2012; Sloan et al. 2012).

But it is a difficulty.

But there is a difficulty.

Here there is a difficulty.

But there's a difficulty.

But there is a difficulty here.

The slowness is a difficulty.

There is a difficulty, however.

But there was a difficulty.

However, there is a difficulty here.