The argument made in the paragraph is the last sentence of the paragraph.
1 – Correct
The last line of the assumes that gripping objects underwater could be advantageous to us.
2 – Wrong
Although this may be true, it is irrelevant to the argument made in the paragraph.
3 – Correct
This is one of the fundamental principles of evolution. Advantageous characteristics must have evolved because they were advantageous. Hence, this must have been assumed in the paragraph.
Statements 1 and 3 are assumptions and hence, D is the answer.