The answers are C and E.

The sentence contrasts the actual daily routines of field botanists with the romantic image of an explorer cutting through an unknown jungle.
The activities listed (cataloguing specimens, measuring leaf geometry, recording soil conditions) are useful and important, but compared with the adventurous image of exploration, they may appear ordinary or dull. The word “yet” then creates the contrast. Although the work may seem boring, the data it produces has transformed our understanding of plant biodiversity. So, the blank must mean ordinary, dull, or unexciting.

A. arduous – incorrect. This means difficult or physically demanding. The sentence is not emphasizing difficulty.
B. hazardous – incorrect. This means dangerous, which would actually match the romantic explorer image more than contrast with it.
C. humdrum – correct. This means boring, ordinary, or lacking excitement.
D. meticulous – incorrect. This means very careful and detailed. The routines may be meticulous, but this does not create the intended contrast with the romanticized explorer image.
E. mundane – correct. This means ordinary, everyday, or unexciting.
F. exacting – incorrect. This means demanding or requiring great care. Again, this may describe the work, but it does not fit the contrast with “romanticized.”