已知向量a＝(1，2)，b＝(2，0)，若向量λa＋b与向量c＝(1，－2)共线，则实数λ＝________．

If，during helicopter refueling operations，fuel is spilled on clothing，the person should first（）.

A.see the medic immediately

B.spray himself with foam or CO₂

C.complete his task and then see the medic

D.remove the clothing and wash