Answer:
C. clearing of ash juniper trees for farmland
Step-by-step explanation:
Golden-cheeked warblers will be in more danger if "clearing of ash juniper trees for farmland" will increase because juniper trees provide barks to build the nest for Golden-cheeked warblers, if Golden-cheeked warblers will not get enough barks to build the nest, they will not able to reproduce and their population will decrease further.
Hence, the correct answer is "C".