Statement A is incorrect as gymnosperms are the seed plants and all seed plants are heterosporous i.e. they make seeds of two different sizes and sex.
Statement B is incorrect as Salvinia is fern (pteridophyte) while Ginkgo and pinus are gymnosperms.
Statement C is correct as Sequoiadendron giganteum is one of the largest evergreen conifer that can attain the height of 54 m.
Statement D is incorrect as needle shaped leaves of gymnosperms are adapted not to accumulate much snow, presence of waxy cuticle and scelerenchyma protect the underlying mesophyll cells, tightly packed tissues protect the central vein containing vascular tissues. Thus, these leaves are well adapted to withstand the harsh and cold climate.
Hence the correct option is C.