Which environmental problem is affecting tuvalu?
a. drought
b. climate change
c. deforestation
d. desertification

Option B, Climate Change

Explanation:

In Tuvalu, the problem is due to its frequent climatic changes. The nation is witnessing continuous rising sea, storm, greenhouse gas issues, drying up of catchments etc.  

Most of the potable water requirement of Tuvalu is fulfilled by the storage system of the catchments which are getting dried. There is continuous erosion of beaches due to the carrying away of sand from beaches to use it in construction works and also there is excessive deforestation.  

All these devastating factors are causing a climate change in Tuvalu.

Thus option  B is correct

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the answer is b.) hydrogen bonds between bases.