本期内容：

David Cameron set out the case for Britain to join America, France and others in air strikes against Islamic state（伊斯兰国） in Syria. Britain was already a“top-tier” target of IS, he said, and could not “subcontract” its security to its allies. A parliamentary vote is expected next week,if the prime minister is sure of a majority.

词义解析:

set out：陈述

air strike: 空袭

top-tier: 首要的

subcontract：转包