1. The main problem is energy density.

2. The main problem is coping with the aggression.

3. 5 The main problem is, of course, high wind.

4. Why not have an Airworthy B-36 in flying status? The main problem is that only …

5. The main problem is understood to be integrating the software and the microchip decoder apparatus in the receiver.

6. The main problem is to prevent others cashing in before we have had time to market the product.

7. The main problem is that the Fed has not moved with alacrity to implement fully key provisions of the Dodd-Frank financial reforms, which were passed in 2010.