方程x+2y=7在自然数范围内解的个数有（ ） A．无数个 B．2 C．3 D．4

聚乳酸（）。

A．在片剂中常用作稀释剂、黏合剂和崩解剂

B．空胶囊的主要成型材料

C．膜剂常用的膜材

D．由乳酸或丙交酯聚合得到的可生物降解的高分子材料

E．防腐剂

锰矿砂及其精矿

电子商务解决方案的基础框架中， (47) 提供用户和目录管理功能。

思维过程的产生依赖于（）。

A.记忆

B.感觉

C.知觉

D.情感

As for projects and operational work, which of the followings is proper

A．A project is constrained by limited resources and operational works generally have no such constraint

B．Projects and operations differ primarily in that operations are ongoing, projects are temporar

C．Projects are different because the project conclueds when its specific objectives have been attained, while operations are repetitiv

D．Operational works are not defined as a projec