1.   Although the reasons remain unclear, many experts suspect that the increase may be partly the result of growing exposure to new chemicals in the environment.

2.   Although the reasons remain unclear, many experts suspect the increase may be partly the result of growing exposure to new chemicals in the environment.

3.   But even if the current espionage case proves that Chinese spies pilfered American weapons design, Clinton said, there remain reasons to continue to work with Beijing.

4.   But even if the current espionage case proves that Chinese spies pilfered American weapons design, Clinton said, there remain reasons to maintain ties with Beijing.

5.   But if one leaves aside the rhetoric from the fight, two reasons for optimism remain.

6.   But the reason had remained a mystery.

7.   Despite numerous studies to find an explanation, the reason remains debated.

8.   Economic conditions nationwide -- particularly falling mortgage rates -- are reasons housing should remain strong.

9.   Even so, economic conditions nationwide -- particularly falling mortgage rates -- are reasons housing should remain strong.

10.   Here again, the reasons remain obscure.