已知集合M={x|x=3m+1，m∈z}，N={y|y=3n+2，n∈z}，若x₀∈M，y₀∈N，则x₀y₀与集合M，N的关系是（　　）

A．x₀y₀∈M但x₀y₀∉N

B．x₀y₀∉M且x₀y₀∉N

C．x₀y₀∈N但x₀y₀∉M

D．x₀y₀∈M且x₀y₀∈N

There are some warnings in some countries ______ over exploitation of underground water has caused the decline of wetland and increase of desertification.

A．which

B．where

C．what

D．that