By promoting more even income distribution in a developing country, a lower birth rate will（）

单项选择题Most environmental problems exist because adequate measures for preventing them（）in the past.

A．was not taken
B．were not taken
C．didn’t take
D．haven’t taken

单项选择题The riot is said（）by the government’s negligence of the people’s welfare.

A．to have been caused
B．being caused
C．to be caused
D．to cause