Which of the following statements is correct?

Capillaries are the thinnest vessels and are lined by single layered epithelium.

Veins do not have valves in them.

Blood is the chief circulating medium of some invertebrates and all chordates.

Blood is fluid connective tissue and forms 10-15% of the intra-cellular fluid.

Volume of blood is about 5 litres in an adult person and it forms about 17-18% of the total body weight.