题目

(trace) the source of theviruses soon, researchers are making a survey all related persons and creatures. 答案：【1】To trace不等式|a-b|≤|a-1|+|b-1|取等号的条件是（ ）A．（a-1）（a-1）＜0B．（a-1）（b-1）≤0C．（a-1）（b-1）＞0D．（a-1）（b-1）≥0