—These Maths problems are too hard to ______. Can you help me? 

—There are many ways, but the most important is to try your best.

A．work out

B．come out

C．put out

D．look out

属于现代市场营销的基本观念的有（）

A.生产高值产品，并不断改进产品，使之日趋完美

B.以消费者为中心

C.企业需要积极推销，进行大量的促销活动

D.已消费者需要为企业活动的出发点