Sentence:  The yawning gap in neuroscientists' understanding of their topic is in the intermediate scale of the brain's anatomy. Science has a <WSD>passable</WSD> knowledge of how individual nerve cells, known as neurons, work. It also knows which visible lobes and ganglia of the brain do what. But how the neurons are organised in these lobes and ganglia remains obscure. 
Meaning of the word marked with <WSD> tags:  Tolerable; adequate; no more than satisfactory.