cross-pollination and self-pollination

1) the answer is B since cross pollination requires insects such as bee and butterfly as an agent to carry the pollen grain from one flower to another flower. Hence it becomes an drawback of cross pollination. Without them, fertilization can't occur.
Cross pollination is the transfer of pollen grain form one flower to another flower of same spieces by insects. While self-pollination is the transfer of pollen grain from same flower's stamen's anther to its gynoecium's stigma of same spieces by wind.
what are the difference? see the table below
description--------------------cross pollination-----------self pollination
flower size-----------------------large--------------------------small
colour---------------------------colourful------------------------green in colour
require insect for pollination----yes---------------------------------no
amount of pollen grain formed---small-----------------------------large
pollen size----------------------------large---------------------------small
pollen shape--------------------have spike-------------------------smooth
gynoecium-------------------surrounded by petal---------------outside petal
I hope my writing can help you.

1) b. External agent is required is not advantange of cross-pollination over self-pollination.
as cross pollination will result in a greater genetic variation than self-pollination, also, both self and cross pollination require to produce a lot of pollens, so a and c are not the answer. as for b, as cross pollination require an external agent, if it is not available, no pollination and hence fertilization will occur. so b must be the answer.

2) cross pollination is the pollen from one flower fertilize with the ovum of another flower of the same species.
self pollination is the pollen form one flower fertilize with the ovum of the same flower of the same species.
cross pollination VS self pollination
require two flowers<---> require only one flower
need external agent, like insect and wind <---> no external agent is needed
more genetic variation <---> less genetic variation
can be occurs in plant with bisexual flowers and unisexual flowers <---> can only be occured in bisexual flower