旅游活动的基本要素包括（）
A.旅游者
B.旅游吸引物
C.旅游服务
D.旅游设施
参考答案：A, B, C, D
Should RGS (regulator of G protein signaling) proteins be classified as GEFs (guanine nucleotide exchange factors) or GAPs (GTPase activating proteins) Explain what role this activity plays in modulating G-protein-mediated responses in animals and yeasts.
喷涂作业须注要（）.
A.喷料嘴与物面要垂直
B.喷枪必须走成直线
C.喷枪要匀移动
D.喷涂长度以
