[填空题]
This image shows an aphid4 klxs y.7)3eez5ibp c with ljqjvg m 439e 0a0oa4ltf):acits stylet inserted into a plant. Aphids have been used to study 4v)lo 34aa:0jaf90g ljmqct etransport 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.
