Geitonogamy involves the pollen nd stigma of flowers of same plant
3 xenigamy involves cross pollination
4 cleistogamous flowers are do not open at all so b is the correct answer

Cleistogamous flowers are always autogamous.

Explanation:
Cleistogamous flowers are a type of flower that remains closed and self-pollinates. They do not require external agents like insects or wind for pollination. The term "cleistogamy" comes from the Greek words "kleistos" meaning closed and "gamos" meaning marriage.

Cleistogamous flowers have several characteristics that enable them to self-pollinate. These include:

1. Closed flowers: Cleistogamous flowers remain closed throughout their development and do not open up to expose their reproductive organs. This prevents the entry of foreign pollen and ensures self-pollination.

2. Reduced or absent petals: Cleistogamous flowers often have reduced or absent petals, which further restricts access to the reproductive organs. This also helps in conserving energy as petals are not required for attracting pollinators.

3. Self-fertile flowers: Cleistogamous flowers are self-fertile, meaning they have both male and female reproductive organs within the same flower. This eliminates the need for cross-pollination with other flowers.

4. Cleistogamy as a reproductive strategy: Cleistogamy is an adaptive reproductive strategy that allows plants to reproduce even in unfavorable conditions, such as low pollinator activity or limited availability of mates. By self-pollinating, plants can ensure reproductive success and maintain their population.

It is important to note that while cleistogamous flowers are generally autogamous, meaning they self-pollinate, some species may also exhibit a certain degree of geitonogamy. Geitonogamy refers to the transfer of pollen from the anther of one flower to the stigma of another flower on the same plant. This can occur in some cleistogamous species due to the proximity of the flowers or the action of certain pollinators.

In conclusion, the correct statement is that cleistogamous flowers are always autogamous. Cleistogamous flowers are a specialized type of flower that remains closed and self-pollinates, ensuring reproductive success even in the absence of external agents like insects or wind.