He must use this surplus in three ways:as seed for sowing,as an insurance（ ）the unpredictable effects of bad weather and as a commodity which he must sell in order to replace old agricultural implements and obtain chemical fertilizers to feed the soil.

单选题

All persons in this area must use a respirator.

答案解析

单选题

He must use this surplus in three ways:as seed for sowing,as an insurance（ ）the unpredictable effects of bad weather and as a commodity which he must sell in order to replace old agricultural implements and obtain chemical fertilizers to feed the soil.

答案解析

多选题

Which prerequisites must be fulfilled before you can use negative postings? Note: There are 2 correct answers to this question.

答案解析

单选题

Personnel must obey this procedure.

答案解析