Reasons why incumbent senators have greater competition than incumbent members of the house include all of the following reasons
a. an entire state is more diverse than a congressional district, providing more of a base for opposition.
b. voters are less likely to know the issue positions of their senators than their representatives.
c. senators have less personal contact with their constituencies.
d. senate challengers are better funded than house challengers.
e. senators tend to draw more visible challengers.

Except B. Voters are less likely to know the issue positions of their senators than their representatives.

Explanation:

In general Incumbents have system advantages over challengers during elections. For example, they share the timing of elections may be determined by incumbents. Visibility and media also play in favour of them, but mostly for the members of the House who continually expose their positions about different topics and issues. Senators' visibility and media attention are not different from representatives.

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