家兔因哪一项特性而用于胆固醇代谢和动脉粥样硬化症研究（）。A.兔对致病胆固醇的敏感性

A total of 4.6 million digital televisions have been sold, and the sales of HDTV sets have quadrupled since last year. Consumers have bought HDTVs to play their DVDs and to have clearer pictures and wide screens. Only a small percentage of the people who have purchased HDTVs, however, have actually hooked their TVs up to receive high-definition television digital signals. Perhaps television viewers are having trouble keeping up with the changes in technology. Even the manufacturers of HDTVs, like Mitsubishi, Thomson Multimedia, Sony, and Samsung seem to have a tough time learning how to make their sets work with the various digital TV formats because little standardization has been required or implemented in the industry.

Some of the HDTVs weigh over 200 lbs., and a variety of retailers offer a delivery service to the buyer’s home to help install the heavy sets. This is known as a white-glove service and usually comes with an extra fee. After HDTV purchasers get their sets home and hook them up, they will still need to work to get the digital signals to their systems. Most of the industry’s cable providers do not yet offer high~definition programing, and only about 15% of commercial television stations have switched over to even the lowest improved digital pictures. Worse yet, viewers may need to install antenna before they can even get the digital signals to their new HDTV sets. Another frustration for home-theater seekers is that the current HDTV sets allow owners only to watch high-definition programs, not to record them.

According to the first sentence, the sales of HDTV sets since last year, by the time when this article was written, had reached ().

A. 4.6 million

B. 9.2 million

C. 18.4 million

D. I do not know how many

基准物质即是用来标定标准溶液浓度的纯物质。5.

五求标准是什么

某单原子分子理想气体进行卡诺循环时，高温热源的温度为227℃，低温热源的温度为127℃。则该循环的效率为（）。

A．56%

B．34%

C．80%

D．20%

以下不属于职业道德特征的是(　　)。

A．职业性

B．实践性

C．固定性

D．继承性