The first step is to pre-train the model on one MCQA dataset referred to as the source task, which usually contains abundant training data. The second step is to fine-tune the same model on the other MCQA dataset, which is referred to as the target task, that we actually care about, but that usually contains much less training data.  
 Question: How different is the dataset size of source and target?
the training dataset is large while the target dataset is usually much smaller