Carbon has 4 valence electrons and can thus bond to 4 other atoms. Thats why it is called tetravelent. (2 electrons from the 2s orbital and 2 electrons from the 2p orbital contribute to a sp3 valence hybridization allowing carbon to form 4 bonds)
Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features. There are two types of geologic accretion—plate accretion and landmass accretion. The Plate accretion involves the addition of material to a tectonic plate. The Landmass accretion involves the addition of sediment to a coastline or riverbank, increasing land area.
Wind erosion is the main form of weathering in deserts.
The right answer is D.
The effectiveness of BT-Corn compared to conventional insecticide treatment is very much higher:
* The plant itself produces the toxin that blocks the digestion of or target insects: the entire plant is protected where a treatment (out of neonicotinoids, very expensive and reserved to the seed treatment) allows only a protection of surface and must be renewed several times.
* The selectivity of the treatment is very superior: each variant of the BT molecule targets only a family of insects but we do not know the impact of their cumulative effects in the environment.
