At this period the principal difficulty in gas manufacture was purification.

The principal difficulty was, I did not know Latin enough for a priest.

One would not have been surprised if this argument had been used by the friends of the proposition, as an answer to its principal difficulty.

The principal difficulty is in keeping the configuration of the balls stable during the initial drop.

One of the principal difficulties will be that quality control and productivity issues have been historically dealt with at the plant level.

Our principal difficulty is that we have no one trained for the kind of work we're having to do.

My own work offers a model of language which reveals where the principal difficulties lie.

But the principal difficulty was to raise and place me in this vehicle.

The principal difficulty of the project was the amount of land required.

Actually the principal difficulty with the walk was provided by Bob's joints, which were still painful.