肝性脑病病人血液中支链氨基酸浓度降低的机制是（）。

A.支链氨基酸合成蛋白质

B.支链氨基酸经肠道排出

C.支链氨基酸经肾脏排出

D.肌肉等组织摄取、分解、利用支链氨基酸增多

E.支链氨基酸进入中枢神经系统

President Bush arrived in Washington and forged ahead with an ambitious agenda- (1) tax cuts, vast changes in federal social programs, expansions of executive power and (2) broad remaking of energy and education policies.
Claiming a mandate by simply declaring (3) existence, his early successes dazzled his critics. With guru Karl Rove directing the (4) , Bush won a stunning series of political victories.
He muscled his agenda through (5) friendly Congress, and gained seats for his party in the 2002 midterm elections. (6) biggest triumph came in 2004, when he won a second term despite a (7) unpopular war.
The "permanent" Republican majority he and Rove envisioned even seemed attainable (8) Bush plunged himself into his most ambitious legislative effort yet: a partial privatization (9) Social Security.
But the president who boasted about "political capital" in the heady (10) after his re-election now faces the worst of political fates as he enters (11) final year in office: borderline irrelevance.
The president’s second term has (12) defined by legislative paralysis, marked by record-low approval ratings, presidential candidates who are (13) from his shadow, and a lingering war that’s sapping his remaining reservoirs of (14) .
As he enters his final year in office with the war continuing, Republican (15) for president bolting from his shadow, and his party back in the minority (16) Congress, he is politically weakened, an early entry into lame-duck status.
And the (17) Washington atmosphere he hoped to cure is just as nasty as it was (18) he came to office seven years ago.
"lie’s left our political institutions much (19) troubled than they were before," said Thomas E. Mann, a senior fellow at (20) Brookings Institution, a Washington-based think tank. "He didn’t create the ideological polarization, but he magnified it. \