[填空题]
This image shows an aphid with its stylet inserted into a plant. Ap2 rfd2)je .xbuu.mgo) hids hav8gpeg(-xck1r t .rzm0 e been used to study z1 rgxtm .-er(ck0p8g transport in plants.
1.Name the tissue that aphids insert their stylets into.
This tissue is .
2.Outline how scientists use aphids to study the substance transported in this tissue.
3.Explain the differences in the contents and rate of flow of phloem sap at sources and sinks.
