I think it is C. I hope I helped.
Answer:
At an angle of 
Explanation:
Assume the river flows from East to West so for the swimmer to cross across it, assume he crosses it from West to East.
The resultant speed will be given by

Answer:
See the answer below
Explanation:
The optimal conditions for high biodiversity seem to be a <u>warm temperature</u> and <u>wet climates</u>.
<em>The tropical areas of the world have the highest biodiversity and are characterized by an average annual temperature of above 18 </em>
<em> and annual precipitation of 262 cm. The areas are referred to as the world's biodiversity hotspots. </em>
Consequently, it follows logically that the optimal conditions for high biodiversity would be a warm temperature of above 18
and wet environment with annual precipitation of not less than 262 cm.
The variation in temperature and precipitation across biomes can thus be said to be responsible for the variation in the level of biodiversity in them.
I would say by putting two fingers under your chin or putting two fingers on the back of your wrist, hope i helped ! :)