太阳系以19.6km/s的速度向武仙座方向运动,一年内飞过多少天文单位?
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Also known as "digital marketing" and "e-marketing," social media marketing has purpose-built data analytics tools that allow marketers to track how successful their efforts are.()
Cold calling is the marketing process of approaching prospective customers or clients—typically via telephone, by email or through making a connection on a social network—who were just expecting such an interaction.()
Traditional forms of marketing such as newspaper and television advertising, direct mail and cold calling integrate well with the powerful medium of the Internet and have become more and more effective as a result.()
何谓星云和星际物质?星云怎样分类?银河系的形状和结构有何特点?