Negative<br/>externalities cause loss of welfare not transmitted by market<br/>factors.

Assuming<br/>that a vaccine against hepatitis C was developed. To evaluate the<br/>effectiveness of this vaccine, the population that should be<br/>selected as the research object is ( ) A: People<br/>with low incidence of hepatitis C B: People infected with hepatitis C C: People<br/>who have been infected with hepatitis B D: High-risk population of hepatitis C

The Americans cannot ______<br/>ignoring the problem. A: accuse him<br/>of B: accuse him<br/>from C: deny him<br/>of D: deny him<br/>from

飞沫传播：droplet __________

The<br/>main morphological characteristics of serous nuclei are as follows() A: The<br/>nucleus is round, at the bottom of the cell base. B: The<br/>nucleus is oblate, at the bottom of the cell base. C: The<br/>nucleus is round, at the center of the cell. D: The<br/>nucleus is oblate, at the center of the cell. E: The<br/>nucleus is at the top of the cell.